As someone who has just started learning ABC of timeseries can some explain me with real - life examples of what AR (autoregressive) and MA (moving-average) MODELS helps in real life. where AR with order of p follows : $$X_t=\mu + \alpha_1\left(X_{t-1}-\mu\right) + \alpha_2\left(X_{t-2}-\mu\right)+ \dots + \alpha_p\left(X_{t-p}-\mu\right) + e_t$$ where MA with order of q follows : $$X_t=\mu + e_t + \beta_1e_{t-1} + \dots + \beta_qe_{t-q}$$

Can you give some real-life examples of time series for which a moving average process of order $q$, i.e. $$ y_t = \sum_{i=1}^q \theta_i \varepsilon_{t-i} + \varepsilon_t, \text{ where } \varepsilon_t \sim \mathcal{N}(0, \sigma^2)   $$ has some a priori reason for being a good model? At least for me, autoregressive processes seem to be quite easy to understand intuitively, while MA processes do not seem as natural at first glance. Note that I am not interested in theoretical results here (such as  or invertibility).  As an example of what I am looking for, suppose that you have daily stock returns $r_t \sim \text{IID}(0, \sigma^2)$. Then, average weekly stock returns will have an MA(4) structure as a purely statistical artifact.


i'm trying to automate the research about a list of domain i have (this list is a .txt file, about 350/400 lines). I need to give the same command (that uses a py script) for each line i have in the txt file. Something like that:  import os  with open('/home/dogher/Desktop/copia.txt') as f:     for line in f:         process(line)         os.system("/home/dogher/Desktop/theHarvester-master/theHarvester.py -d "(line)" -l 300 -b google -f "(line)".html")    I know there is wrong syntax with "os.system" but i don't know how to insert the text in the line, into the command.. Thanks so much and sorry for bad english..

How do you call an external command (as if I'd typed it at the Unix shell or Windows command prompt) from within a Python script?


In QGIS, I have a mountain range with a valley on either side (DEM raster file). Is there software or a plugin that allows me to calculate the easiest pathway over the mountain? The answers at  are from 3 years ago and involves skills I've not yet acquired. Has nothing been developed in 3 years for us novices? Does QGIS3 not yet offer anything?

Are there any tools, plugins or methods in QGIS which allows for an analysis of the best path between two points using least cost path method? As shown below ArcGIS has several distance tools.


When I try to use terminal, I put in a command and then it asks for my password.  I type my password and nothing comes up on the screen.  Help?

When I'm about to install a program in the terminal it wants the password:  [sudo] password for xxx:   But when I start to type my password nothing happens. What should I do?


Over the last few days I have been having issues with my machine running very slow. The problem seemed to be with the System process consuming about 20% CPU (more specifically ntoskrnl.exe!MmProbeAndLockPages).  Many attempts to reset and/or reinstall where unsuccessful. The only options that eventually worked was to reinstall windows (fresh) with the Network cable unplugged. This prevented Windows updates during the installation.  Now, I'm quite certain it's one of the device driver updates that's causing this issue. I have Windows Updates disabled for now but I would like to turn it back on but run the updates in stages.  Is there a way to selectively approve updates one by one? I am running Windows 10 Pro on a home network (if it makes a difference).  Thanks!   EDIT: I think I have managed to find the problem. I've enabled Windows Update again and it went through the same process of updating drivers. Checking the list of drivers I went to the Lenovo support website (M93p in my case) and started downloading alternative drivers and install them one by one. The Intel Gfx Driver fixed the problem and now the computer is responsive again. The high CPU from the System process may have been unrelated.

I have noticed that from some time my system is freezing and its probably caused by the high CPU usage which is caused by the system process.  All applications I'm running is the Skype, TeamSpeak and Chrome so it definitely shouldnt eat that amount of CPU.  You can see the problem itself and running processes in the screenshot below:    Sometimes CPU usage is reaching 90%, but the average usage is like 40-65%.  My PC parameters:   Windows 8 (customer preview) Intel Core i3 - 2350M 8 GB RAM   I'd appreciate any help attempt! Regards.  --UPDATE--  As the user below posted a great answer, I have noticed that the process that is eating the most CPU in the system is called Arthurx.sys, simple google tells that it's a TPLink driver (an wifi adapter, I have bought like 2 weeks ago!) drivers has been installed from the Windows MSDN, but also tried to install the drivers from the attached CD, but it doesn't help. From the system start, it is using like 5% of the CPU only, but after 2-4 hours of working it is growing up and reaching 40-60% of the CPU usage.  Device name: TPLink WN722N


We are currently in the process of installing a new Wi-Fi repeater in our house. Our house was built with Cat5e cabling in the walls, conveniently going from the location of our current router to our new bridge. Since I'm not about to go into my walls and change out the Cat5e cabling for Cat6 cabling, is it worth connecting the access points to the wall tap using a Cat6 cable, or do you have to go completely Cat6 for any benefit?

I was wondering if I can use a CAT5e keystone jack with CAT6 cable. I am refering to the parts that terminate a cable where it comes out of the wall.  I want to run a 30 ft length of CAT6 but all I have is CAT5e jacks and I don't want to buy any news ones if I don't have to.  I had read somewhere that CAT5e is 100mhz and CAT6 is 200mhz (though I could have sworn CAT6 was 350mhz).  Anyhow any assistance would be appreciated.


Why does the captain order the passengers to open the window shields on an air plane when taking off or when landing?  I've asked the flight attendents many times. The answer has always been the most annoying one:  "This is the rule."  But why????

I have always wondered why the windows shades have to be raised during take off and landing. I can't think of any safety issues by having a closed window.


I decided to randomly take a look at my /etc directory, and I saw some entries like this:  passwd passwd- shadow shadow- subgid subgid-   I know they are hyphens (-) and not tildes (~). What are the files with a hyphen suffix for (as opposed to their non-hyphened counterparts)?

Possible Duplicate:          I have a strange passwd- file in /etc, notice the trailing dash:  root@ubuntu:~# ls /etc/passw* /etc/passwd  /etc/passwd-   Notice the different permissions:  root@ubuntu:~# ls -hl /etc/passw* -rw-r--r-- 1 root root 2.0K Oct 26 13:38 /etc/passwd -rw------- 1 root root 1.9K Oct 26 13:38 /etc/passwd-   and the difference in content:  root@ubuntu:~# diff /etc/passwd{,-} 39c39 < mysql:x:119:129:MySQL Server,,,:/nonexistent:/bin/false --- > mysql:x:119:129::/nonexistent:/bin/false   What's happening here?  root@ubuntu:~# uname -a Linux ubuntu 3.2.0-29-generic-pae #46-Ubuntu SMP Fri Jul 27 17:25:43 UTC 2012 i686 i686 i386 GNU/Linux root@ubuntu:~# cat /etc/issue Ubuntu 12.04.1 LTS \n \l


why output so strange 0022 =18? hello everyone to day i have test.the question is "what is the output of   System.out.println(0022);   i so confuse why Answer is 18   explain needed

This prints 83  System.out.println(0123)   However this prints 123  System.out.println(123)   Why does it work that way?


I am the fresh owner of my first DSLR (a Canon EOS 600D, as far as I know called Rebel T3i in the USA). I'm a total newbie, and the camera is a lot smarter than me most of the time. But I'm trying to learn how to choose the settings for certain situations myself (in particular when it comes to lighting) instead of leaving stuff to the electronics.  Now, I understand the theoretical basics of the influence of exposure time, ISO, and aperture size on the resulting image, but knowing the theoretical basics of a combustion engine doesn't enable me to drive in the Indy 500.  So I'm trying to take pictures here and there and looking at results etc., and now I have a situation where I have no idea what to do. The example is probably silly; this is more a "I'd love to know how it works" than a "this is an actual problem I need solved".  I have a ceiling lamp (essentially a tinted glass ball) that has a very nice structure to it and gives the (white) ceiling above it a nice orangy-red glow. Capturing the structure is doable:   (f/5.6, 1/500s, ISO100)  Getting the nice glow is probably possible as well, by finding something between these two and adjusting the white balance:   (1: f/5.6, 1/125s, ISO 800; 2: f/5.6, 1/60s, ISO 3200)  (yes, the aperture is identical among all three images; I also tried slower ones, but didn't get any noticably different results).  So usually I'd say "well yeah, it's impossible; you have a glass structure with a bright light bulb behind it, and a dimly lit ceiling; no way you're getting those two nicely into a single image". But over the past few days since I started trying to learn about photography, I've read up on so many ways to play with how light reaches the sensor, that I wouldn't be too surpised to learn I can actually achieve both.  Can I?  Note that I'm interested in doing this in one shot; I can obviously combine two different images during post-processing, but I'm interested to learn "tricks" to achieve this in a single shot.

I am quite new to photography and was looking into how I can take better indoor photographs, particularly around night time.  I'm currently in a hotel room for the night and decided to try and take a picture of my room to test out my tripod which I haven't used before. However I noticed no matter what I set my camera settings to the artificial lights (particularly the lamp on the left, image attached) just appeared very washed out. You can't tell any detail about the lamp shade all you can see is just some sort of light but not much to it.  I tried a variety of fstop/shutter speed settings and tried a variety of ISO settings but they all appeared pretty much the same unless I massively underexposed the image.  Given that I wondered whether the solution would be to take a HDR image or take a normal exposure and an underexposed image and blend them later? I understand that artificial light like this can be very hard and harsh but I wondered if there's a way of improving the result with looking away from it?  I wasn't trying to take any particular special picture here but just test out my camera a bit more but this was the first thing I noticed and I didn't know how to fix it. Any tips would be greatly appreciated.


Given the points of the vertices of a triangles as tuples (x,y) and a point P=(x,y).  How can I determine if this point P is contained in the triangle (assume that it's not on the border of the triangle)?

Is there an algorithm available to determine if a point P lies inside a triangle ABC defined as three points A, B, and C? (The three line segments of the triangle can be determined as well as the centroid if they are needed.)  Grid space is defined as Screen Space, that is, 2D Cartesian with the Y-Axis flipped so "up" is negative y and the origin is the upper left corner.


Show $f(x) = x^2 \sin (x^{-3/2}), x\in (0,1] $, $f(0) = 0$ is of bounded variation.     Try  $\forall P = \{0 = x_0 < \cdots, < x_n = 1\}$, $\exists c_k \in (x_{k-1}, x_k)$ s.t. $f(x_k) - f(x_{k-1}) = f'(c_k) (x_k - x_{k-1})$$(\because MVT)$.  Thus,  $$ V(f, P) = \sum |f(x_k) - f(x_{k-1})| = \sum |f'(c_k)| (x_k - x_{k-1}) $$  I think the next step should allow me to prove the RHS is less than some value. However, observing the following,  $$ f'(x) = \begin{cases} 2x \sin(x^{-3/2}) - \frac{3}{2} x^{-1/2} \cos(x^{-3/2}) & (x \neq 0 ) \\ 0 & (x=0) \end{cases} $$  I have $|f'(x)| \le 2x + \frac{3}{2}x^{-1/2}$, but RHS is not bounded on $[0,1]$.  Any help, including one that excludes the use of improper integral, will be appreciated.

I'm trying to show that $F(x)=x^a\sin\left(x^{-b}\right)$ for $0<x \leq 1$ and $F(0)=0$ has bounded variation only if $a>b$.      I know I have to show there exist an $M< \infty$ such that for any partition $0=t_0<t_1<...<t_n=1$ we have  $$\sum_{j=1}^N |F(t_j)-F(t_{j-1})|<M \iff |F(t_1)| + \sum_{j=2}^N |F(t_j)-F(t_{j-1})|<M .$$  I'm stuck here.


I've been stuck on this prelim problem for a while. I'm not sure how to start. I tried playing around with simple functions, but I can't relate $\psi(t)$ to $g$.     Let $g:X\to[0,\infty)$ be a measurable function and $\psi(t)=\mu\{x \in X : g(x) > t\})$. Prove that   $$\int_X\!g\,\mathrm{d}\mu=\int_0^\infty\!\psi(t)\,\mathrm{d}t.$$

Let $f$ integrable and let $E_\alpha=\{x\mid |f(x)|>\alpha\}$ for $\alpha\geq 0$. Show that $$\int\left|f(x)\right|dx=\int_0^\infty m(E_\alpha)d\alpha$$ where $m$ is the Lebesgue measure.   By hypothesis, $f$ is measurable, therefore there exists a sequence of simple function such that $\varphi_n\nearrow |f|.$ Moreover, $E_\alpha^n\nearrow E^\alpha$. By the continuity of the measure, $m(E_\alpha^n)\to m(E_\alpha)$ for all $\alpha\geq 0$. By the convergence monotone theorem, $$\int_0^\infty  m(E_\alpha)d\alpha=\lim_{n\to\infty }\int_0^\infty  m(E_\alpha^n)\underset{(*)}{=}\lim_{n\to\infty }\int\varphi_n(x)dx=\int\left|f(x)\right|dx.$$   I don't understand the equality $(*)$, why $m(E^n_\alpha)=\varphi_n(x)$ ?


I read the subject book in 1981 and it wasn't new then. The book probably would be described today as a space opera.  From what I can remember there is an intersolar system war between two solar system races NOTE humanoid, not human. One planet is eventually destroyed  (the asteroid belt) and the other is laid waste...  There is a colony on the dark side of the moon that is destroyed in a massive meteor storm with the survivors walking to rescue on the moons surface gradually dying off until only # one makes it through sheer bloody minded determination to the rescue site where a small number of survivors revamp to earth Now the story swaps back and forwards with many reverses and twists but in the end archaeologists find the one walkers equipment buried for over 2000 yrs...aka  our forefathers..  And that's what I can remember, the story is intense and the revelations during the book are stunning I seem to remember.

If I recall it correctly, this book has two main characters, both male, one of them big and well muscled. During the novel, they found evidence that the current human race descends from ancient Martian astronauts who traveled to Earth in prehistory, causing the extinction of prehistoric Earth humans, (which explains the Missing Link in human evolution).  Later in the novel the big guy travels back in time (no idea of how or why) to Prehistory.  And near the end of the book, the other main character, during an archaeological field research, finds remains of a human being who lived thousand of years ago, a human with large bones, and who holds an item that could not be made in that era (a gold plaque? A metal rod?)  That's all I can remember. I know it is not from the ABC, Asimov, Bradbury or Clarke.  Thanks in advance.


How do I draw this function on Tikz or any other alternative??

When i plot the graph of $(x^2+x+1)/(x+1)$, there appears to be a solid vertical line in the plot which happens to be the vertical asymptote, is there a way to make that line dotted and also include the oblique asymptote in a similar fashion?  \documentclass{article} \usepackage{amsmath} \usepackage{pgfplots}  \begin{document} \begin{tikzpicture} \begin{axis}[     axis lines = center,     xlabel = $x$,     ylabel = {$y$},     xmax = {5},     xmin = {-5},     ymax = {5},     ymin = {-5},     legend pos = outer north east ] \addplot [     domain=-10:10,      samples=100,      color=black, ] {(x^2+x+1)/(x+1)}; \addlegendentry{2 turning points} \end{axis} \end{tikzpicture} \end{document}


I'm a week into making apple cider vinegar. I've used jars and the apples at the top were not covered with liquid. A blue mold formed. I've removed it. Should I carry on or should I start again? If I carry on would the final resulting vinegar be OK for consumption? Or just topical application? Any advise greatly appreciated. Hate to Waste!

About 2-3 months ago I decided to start my own batch of vinegar.  I started with some Braggs apple cider vinegar which contains the mother, and I added some old wine and some fruit juice to the mix.  I kept it in a dark and warm place, as per instructions online.  A few layers of cheesecloth were placed on top to allow it to air, without letting anything else get into it.  When I recently opened it, I found a layer of what appears to be a yellow-orange mold on top.  There are also some small worms or maggots living on the top, but that doesn't seem as problematic to me.    As you can (sort of) see in this picture above, there is definitely a mother at the bottom.  The mother has grown since I last saw it.  I am not sure what to think about that top layer though.  Is the vinegar batch completely spoiled?  Picture #2 (a closer look at the top)


I was trying to understand how the calculations are done behind lm() function in R using mtcars dataset. I understand that lm() function minimizes the sum of the squared residuals to get the best fit line. Now the summary() done on that fit gives coefficient which includes: the intercept, slope, standard error, t-statistic, and P-value.  Suppose I fit a regression line with the mtcars dataset using 2 different approaches:   when I don't shift the x=wt axis  library(ggplot2) g <- ggplot(data=mtcars, aes(x=wt,y=mpg)) g <- g+geom_point(size=2, color="blue", alpha=0.4) g <- g+geom_smooth(method = "lm") g <- g+ggtitle("Normal") g <- g+labs(x ="wt", y = "mpg") g    when I center the x=wt axis first:  library(ggplot2) g <- ggplot(data=mtcars, aes(x=c(wt-mean(wt)), y=mpg)) g <- g+geom_point(size=2, color="red", alpha=0.4) g <- g+geom_smooth(method="lm") g <- g+ggtitle("Shifted") g <- g+labs(x="wt", y="mpg") g      So it is evident from the plots that the:   Slopes are same (I understand that)  intercepts change due to shifting of x-axis (I understand that)  But the intercept's standard error in summary(fit) changes (I don't understand this)   Does it mean, the standard error outputted by the summary() function is the standard error in the response only at that x-value? and that this standard deviation will be different at different predictor values?

The standard error of the intercept term ($\hat{\beta}_0$) in $y=\beta_1x+\beta_0+\varepsilon$ is given by $$SE(\hat{\beta}_0)^2 = \sigma^2\left[\frac{1}{n}+\frac{\bar{x}^2}{\sum_{i=1}^n(x_i-\bar{x})^2}\right]$$ where $\bar{x}$ is the mean of the $x_i$'s.  From what I understand, the SE quantifies your uncertainty- for instance, in 95% of the samples, the interval $[\hat{\beta}_0-2SE,\hat{\beta}_0+2SE]$ will contain the true $\beta_0$. I fail to understand how the SE, a measure of uncertainty, increases with $\bar{x}$. If I simply shift my data, so that $\bar{x}=0$, my uncertainty goes down? That seems unreasonable.  An analogous interpretation is - in the uncentered version of my data, $\hat{\beta}_0$ corresponds to my prediction at $x=0$, while in the centered data, $\hat{\beta}_0$ corresponds to my prediction at $x=\bar{x}$. So does this then mean that my uncertainty about my prediction at $x=0$ is greater than my uncertainty about my prediction at $x=\bar{x}$? That seems unreasonable too, the error $\epsilon$ has the same variance for all values of $x$, so my uncertainty in my predicted values should be the same for all $x$.  There are gaps in my understanding I'm sure. Could somebody help me understand what's going on?


Like the title says, i need to find the difference of integers in a list by 2 and must return a list with tuples.   initial_list = [1, 2, 3, 4] expected_output = [(1, 3), (2, 4)]   I wrote this code:  arr = [1, 2, 3, 4] n = 2 arr1 = [] for i in range(len(arr)):     x = i + n     if x in arr:         arr1.append(x) print(arr1)   But doesn't work...  Can u help me?  Thx

I have a list of arbitrary length, and I need to split it up into equal size chunks and operate on it. There are some obvious ways to do this, like keeping a counter and two lists, and when the second list fills up, add it to the first list and empty the second list for the next round of data, but this is potentially extremely expensive.  I was wondering if anyone had a good solution to this for lists of any length, e.g. using generators.  I was looking for something useful in itertools but I couldn't find anything obviously useful. Might've missed it, though.  Related question:


I have a NVidia GTX 1060 6GB Edition GPU. When I try rendering my scene, I get that error. It peaks at only 5GB, meaning I still have 1GB of memory left. However, I'm still getting the error. I could just render with my CPU, and I have, however, I really want to use my GPU because it renders like 3x faster. Any ideas that could help?

I've been struggling a little with Cycles and my GeForce GTX 750 graphic card. Most of the time it works well, but when I try to work with scenes that have custom shaders (like a skin shader with multiple textures, including for displacement), I get an error, both on the viewport and at rendering:     Cancel | CUDA error: Out of memory in cuLaunchKernel(cuPathTrace, xblocks, yblocks, 1, xthreads, ythreads, 1, 0, 0, args, 0)   Or something like that. Here's a screenshot so you can check it out:    I'm using a PC and Windows 7, with 8Gb of RAM. I can't render this scene with GPU, but using CPU, it renders ok.  My question is: What is causing this issue? I have the latest drivers installed for my graphic card, so I have no idea what this is.


I connected my Oracle database to ArcGIS and added one layer to map. This layer has points and polygons. I make a selection in this layer and get 9508 selected features, which I want to export as shapefile and add it separately to the map. I choose Data > Export Data, choose to export only selected features. But in the shapefile I get, there are less objects that were selected - only polygons, not points.   How can I properly create such layer file with selected points and polygons from Oracle database layer?

Does the shapefile support mixed geometry types (ie. point and polygon all in the same file)?


I submitted a paper to a journal and after 20 days I got an email which states  Your submission entitled "X" will be handled by Receiving Editor.  What does this mean?

The web page of my article in the AMS editorial system for some three months says "Article status: Reviewing" and in the next line "Your paper is being handled by an editor". I find this confusing as the "reviewing" status appears to suggest that the article is with the referee(s) rather than with the editor but this in turn seems to contradict the line "Your paper is being handled by an editor".  Could someone with enough experience with AMS journals please explain how should one interpret the combination of "Article status: Reviewing" and the line "Your paper is being handled by an editor" at the article page? More broadly, which are the possible article statuses in the AMS editorial system?  Many thanks in advance.


I am a new user of Ubuntu. A while ago attempted to install Ubuntu alongside Windows 7 but it didn't work. It installed Ubuntu but deleted all the Windows file and I did everything correctly.  Now, I am new to the Ubuntu world and I like the OS and I would like to keep it and learn more but since my desktop is not used only by me, I need to install Windows 7 to dual-boot alongside Ubuntu.  Is there any guide on how to do that?  I have got only one USB stick to save something and I don't even know how to download the Windows ISO file.

I want to install Ubuntu 13.10 on my pre-installed windows 7 pc and I want a dual boot. I have no empty partition on my hard disk drive. I don't want to re-install windows 7 and don't want to install ubuntu on c drive. I want to install on a different partition but I want to resize it. How should I do it? Please answer in steps. Also suggest the amount of space I should allocte to ubuntu 13.10.


I'm hoping this is the correct place to ask.   Basically, I'm using cmus and have a little bash script to automate downloading, renaming and moving a mp3.   However, cmus just lists the song name as its full path in the library (e.g.: /home/user/music/genre/song.mp3)  I'd like to change this by adding tags such as album, title, and artist to the mp3 files.   I'm not sure if in Unix some files inherently have metadata like this or if you have to create the data in a specific way for the music player to be able to read it.   I read the  and I don't see anything about how it reads tags or labels.  Overall, through a bash script after reading an input, such as 'albumname' I'd like to know how to assign that input as the album tag of a mp3 file for a music player to use.

In windows music files have metadata like artist name, album name associated with them. How is this metadata stored. Is it stored in file system like other file attributes or is it part of MP3 data that Windows Explorer extracts using a MP3 reader plugin?  Is it possible to read/change this information in Linux? Is it possible with commandline?  (I know these attributes can be set using Rhythymbox or some music player but I'm curious if these could also be set directly. Like in Windows the windows itself shows you artist information if you right click the file and open properties dialog)


As you see in the image, The &nbsp content is adding to the pages. these are not there in the actual code.

So just now, I had a bug in my site that caused my custom navigation bar's buttons to be sized and spaced incorrectly. I had no idea where this bug came from, and had to search around for awhile to find the answer. It turns out that SharePoint decided it would be a good idea to inexplicably add a few lines of:  nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;  nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;nbsp;   between my   in my DevHome.aspx (I'm using Angular for this particular project). So, why does Sharepoint do this, and how do I prevent it? This is not the first time SharePoint has randomly added an nbsp to my page.  Thanks in advance.


On Meta Islam I posted , which seemed perfect in the preview below the edit box.        But when I posted the question I got something partially different:

that I posted on Meta.Programmers was rather broken, with a block quote replaced by apparently random letters and numbers. Aarthi fixed it with a non-breaking space, but I don't understand what went wrong.  When I opened the post for editing, the displayed text was what I intended to go there. It only happens when the post is viewed in the reading mode. The preview also displayed the text correctly.


In physics, we often describe the dynamic properties of fields using variational principles like defining an action or a Lagrangian. A field however is simply some function of space $\phi(x)$ so I wonder what kind of properties the dynamics must follow to lend itself to description by an action principle? For example, can all dynamics that are continuous be described by some specific action? Just want to get an idea of the restrictions.

We see variational principles coming into play in different places such as Classical Mechanics (Hamilton's principle which gives rise to the Euler-Lagrange equations), Optics (in the form of Fermat's principle) and even General Relativity (we get Einstein's equation from the Einstein-Hilbert action). However, how do we explain this very principle, i.e., more mathematically, I want to ask the following:      If I am given a set of generalized positions and velocities, say, $\{q_{i}, \dot{q}_{i}\}$, which describes a classical system with known dynamics (equations of motion), then, how do I rigorously show that there always exists an action functional $A$, where    $$A ~=~ \int L(q_{i}, \dot{q}_{i})dt,$$    such that $\delta A = 0$ gives the correct equations of motion and trajectory of the system?    I presume historically, the motivation came from Optics: i.e., light rays travel along a path where $S = \int_{A}^{B} n ds$ is minimized (or at least stationary). (Here, $ds$ is the differential element along the path). I don't mind some symplectic geometry talk if that is needed at all.


I have created a database for poll application called poll and tables called polls and users.  When I added SQL for second question:  INSERT INTO `poll`.`polls` (`id`, `question`, `starts`, `ends`) VALUES ('2', 'What''s your favourite web language?', NOW(), '2015-08-12');   Warning from title comes up. Here is export:  -- phpMyAdmin SQL Dump -- version 4.2.12deb2 -- http://www.phpmyadmin.net -- -- Host: localhost -- Generation Time: Aug 10, 2015 at 02:46 PM -- Server version: 5.5.44-0+deb8u1 -- PHP Version: 5.6.9-0+deb8u1  SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO"; SET time_zone = "+00:00";   /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */; /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */; /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */; /*!40101 SET NAMES utf8 */;  -- -- Database: `poll` --  -- --------------------------------------------------------  -- -- Table structure for table `polls` --  CREATE TABLE IF NOT EXISTS `polls` ( `id` int(11) unsigned NOT NULL,   `question` text,   `starts` date DEFAULT NULL,   `ends` date DEFAULT NULL ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;  -- -- Dumping data for table `polls` --  INSERT INTO `polls` (`id`, `question`, `starts`, `ends`) VALUES (1, 'What do you think about new whey protein?', '2015-08-10', '2015-08-12'), (2, 'What''s your favourite web language?', '2015-08-10', '2015-08-12');  -- -- Indexes for dumped tables --  -- -- Indexes for table `polls` -- ALTER TABLE `polls`  ADD PRIMARY KEY (`id`);  -- -- AUTO_INCREMENT for dumped tables --  -- -- AUTO_INCREMENT for table `polls` -- ALTER TABLE `polls` MODIFY `id` int(11) unsigned NOT NULL AUTO_INCREMENT,AUTO_INCREMENT=3; /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */; /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */; /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;   Is it caused by second questions' apostrophe sign?  EDIT: This is not duplicate because I'm doing this in phpMyAdmin and I know what is SQL injection :)

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to , like in the following example:  $unsafe_variable = $_POST['user_input'];   mysql_query("INSERT INTO `table` (`column`) VALUES ('$unsafe_variable')");   That's because the user can input something like value'); DROP TABLE table;--, and the query becomes:  INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')   What can be done to prevent this from happening?


We all know Snape was a double agent (Death Eater and working with Dumbledore), but in the Sorcerer's Stone, he had no idea that Voldemort had latched himself onto Quirrell. This is evidenced in that that Snape is suspicious about some of the actions that he linked to Quirrell, and also confronts him about. But in the scenes that we see them talking privately, they never talk about Death Eater stuff.  I have not read the books and maybe there are talks of it in there, somewhere. But I think it would ruin the whole 'Snape is actually a good guy' plot line, so is that the only reason Voldemort did not expose himself to Snape?  Snape was also one of Voldemort's 'trusted' followers, because he let him get the teaching job at Hogwarts to spy on Voldemort (according to my sources).  It just did not make sense to me after looking a little into the Harry Potter series and re-watching the movies and this was the first thing that struck me as odd.   Why didn't Quirrell tell Snape about Voldemort?

I read something online that got me thinking about this. Why didn't Voldemort suspect Snape had defected from the Death Eaters and was now working for Dumbledore during the events of *Philosopher's Stone?  Voldemort was possessing Quirrell's body and his head was protruding from the back of Quirrell's - in other words, Voldemort was with Quirrell constantly during the events of Philosopher's Stone, presumably overhearing whatever Quirrell himself heard.   Snape cornered Quirrell more than once (Halloween, when Quirrell let the troll in, and the night Harry broke into the Restricted Section over the Christmas holidays to look for information on Nicholas Flamel) and openly threatened him against working for Voldemort and pressuring him to declare his loyalties to Dumbledore. This obviously revealed Snape's loyalty to Dumbledore to Quirrell, and presumably Voldemort, and I can't think of a reason why Voldemort wouldn't have been able to hear Snape strong-arming Quirrell perfectly clearly.   Why didn't Voldemort attempt to make contact with Snape during Philosopher's Stone? After all, Snape was supposedly Voldemort's most faithful servant. How is it Voldemort didn't suspect Snape was working for Dumbledore and didn't orchestrate a move against him? Snape wasn't even pretending to be a double agent during Philosopher's Stone, so why Voldemort didn't kill Snape as soon as he was physically able, or have Quirrell attempt to kill him, is unclear.  So yes, why didn't Voldemort suspect Snape as a double agent during the events of Philosopher's Stone?


I have a table with 3 columns:  \begin{tabular}{|c|c|c|} \textbf{C1} & \textbf{C2} & \textbf{SUM} \hline 2 & 3 & 5 \end{tabular}   But, if I change C1 or C2, I have to change SUM manually. In excel, I can use function like =C1+C2, then SUM will update automatically when C1 or C2 changed. Can latex do that?

I wonder if this feature is available in TeX system? For example, given a formula within a table, it can apply the formula and display data after the calculation.


Stack Overflow  to work through , but the custom avatars (uploaded files, not those from gravatar) are even then fetched from  using standard   (which generates warning in browsers and is not a very good practice). As those images are also available   it could be just a service misconfiguration.  Is there a technical (or any other) reason why they couldn't be fetched using HTTPS?

So it looks like Stack Exchange now supports HTTPS (to some extent). Which is awesome! But there are a few problems, the main one being that some content is delivered over the CDN, which is plain HTTP. This causes browsers to complain about "unsecured content":


I have a file named #%2Amerge%2A#4984jjK#.   # starts a comment in bash. So how can I remove the file?  Thanks.

I was running a Python script that malfunctioned and used sudo to create a file named >.  How can I get rid of this file?  Of course, when I try sudo rm >, I get the error bash: syntax error near unexpected token 'newline', because it thinks I'm trying to redirect the output of rm.  Its permissions are -rw-r--r--.


You can use \tikzsytle{mystyle}=[some options]; to define a custom mystyle globally, that means it affects all tikz graphics in the document, but is there also something similar if you want to define a custom mystyle just within one tikzpicture?

The PGF/TikZ manual states in section 12.4 Using Graphic Options, page 120 (v2.10), that TikZ styles can be set using:  \tikzset{my style/.style={<tikz options>},...}   However, in several places in the same manual the otherwise undocumented macro \tikzstyle is used for settings styles:  \tikzstyle{my style}=[<tikz options>]   I also have seen this usage in several online code examples.  Why are there two ways to set TikZ styles and which one should be used for new code?  Note: I actually know the answer but think that such a question with good answers would be beneficial for other users.


I have installed Ubuntu 18.04 in Lenovo Ideapad 330. After installation Wireless LAN adapter is not working. Output of lspci -knn | grep -i Net -A2:  03:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe Wireless Network Adapter [10ec:c821] Subsystem: Lenovo RTL8821CE 802.11ac PCIe Wireless Network Adapter [17aa:c024]

We just bought a Lenovo  (which is supposed to have the Intel 8265 for wireless). This laptop was bought in part because it is certified to run Ubuntu and as such to me at least it would make sense for things to work out of the box... but no such luck.  First, I installed Ubuntu 17.10 and after installation realised Wi-Fi was not working. I also tried Ubuntu 16.04 from a USB drive since that is the version of Ubuntu it is certified for, but no luck there either.  The wireless chip is not detected by lshw (or even lspci by the looks of it), ip link does not show a wireless interface, and the iwlwifi kernel module is not loaded at boot (I can load this myself using modprobe iwlwifi but this does not make Wi-Fi work). I think it is a combined Wi-Fi/Bluetooth chip, and Bluetooth does appear to work (or at least Bluetooth shows up in Gnome and rfkill list).  modinfo iwlwifi | grep 8265 shows me a file ending in -34 is supposedly loaded but only a file ending in -33 (and some other lower numbers) is present in /lib/firmware, if that helps).  I have also installed the Linux 4.14.9 kernel in an attempt to get things to work, but this did not resolve the issue either.  Further information  root@ThinkPad-E570:~# modinfo iwlwifi | grep 8265 firmware:       iwlwifi-8265-34.ucode root@ThinkPad-E570:~# rfkill list all 0: tpacpi_bluetooth_sw: Bluetooth     Soft blocked: no     Hard blocked: no 1: hci0: Bluetooth     Soft blocked: no     Hard blocked: no root@ThinkPad-E570:~# dmesg | grep iwl root@ThinkPad-E570:~# lspci -nnk | grep 0280 -A3 05:00.0 Network controller [0280]: Realtek Semiconductor Co., Ltd. Device [10ec:c821]     Subsystem: Lenovo Device [17aa:c024]   Update  I just noticed that the laptop does not have an Intel wireless chip at all, but in fact has a Realtek one... which means that the  of the shop I bought this laptop at were not accurate... Sigh. Same problem stands, however, just with a crappier wireless chip.


Let $p$ be a prime number. Consider for all $k,r\in\mathbb{N}_0$ with $k|r$ the field $\mathbb{F}_{p^k}$ as a subfield of $\mathbb{F}_{p^r}$. Define $$ \overline{\mathbb{F}_p}:=\bigcup_{i\in\mathbb{N}_0}\mathbb{F}_{p^i}.$$ I want to show that $\overline{\mathbb{F}_p}$ is the algebraic closure of $\mathbb{F}_p$. I already managed to show that $\overline{\mathbb{F}_p}$ is a field and that it is algebraic over $\mathbb{F}_p$, but I can't seem to show that it is also algebraically closed. I know that for every $i\in\mathbb{N}_0$, $\mathbb{F}_{p^i}$ is a decomposition field of the polynomial $X^{p^i}-X$. Which means this polynomial can be expressed as $$X^{p^i}-X=\prod_{a\in\mathbb{F}_{p^i}}(X-a),$$ and I thought that this could help me prove that every irreducibel polynomial in $\overline{\mathbb{F}_p}[X]$ has degree $1$ but so far it hasn't. Any help would be appreciated.

I'm proving that $\overline{\mathbb{F}}_p = \bigcup\limits_{i=1}^{\infty} \mathbb{F}_{p^i}$ is an algebraic closure of $\mathbb{F}_p$ where $p$ is a prime. I think I've gotten down how to prove that $\overline{\mathbb{F}}_p$ is a field and that it is algebraic over $\mathbb{F}_p$. I have some difficulties with proving that $\overline{\mathbb{F}}_p$ is algebraically closed. My attempt is as following: Suppose $f$ is a non-constant polynomial in $\overline{\mathbb{F}}_p [X]$. If $\overline{\mathbb{F}}_p$ contains a root of $f$, then it is algebraiclly closed. Per definition there must exist a $\mathbb{F}_{p^k}$ for a certain positive integer $k$ that contains all the coefficients of $f$. Take a root $\alpha$ of $f$ and consider the extension $\mathbb{F}_{p^k}(\alpha)$. How is this now a field of the form $\mathbb{F}_{p^l}$ for a certain positive integer $l$?


I have a castle in the sky. It is made completely out of stone bricks and walls. I have met ALL the requirements necessary and am still told it is not valid. I have 6 rooms in the upper part of my castle, 3 on the left-which are completely symmetrical to the 3 on the right. The rooms in the top corners are (from the inside of the walls) 7x4. The roomes in the middle are ("  ") 8x4. And the rooms on the bottom are ("  ") 10x4.  The top rooms are high enough that it just barely starts to turn into space and while that could be the problem, Steve the Guide used to live in the upper left corner. I left that world and when I came back, Steve was in a different room and his old one said it was invalid. The one right below it is also having problems even though I have Durim the demolitionist in the room on the opposite side.   Like I previously mentioned, I made the rooms on the right completely identical to the ones on the left. Complete with stone brick, stone walls (of which I went over again), 1 torch, 1 chair, 1 table/workbench and plenty of floor space. I don't have any platforms  in the rooms and yes I have a door leading to each one. Thanks in advance for your help! :)

I read on the wiki that people will move in under the following conditions:   You do something to please them An empty house is available with a light source, table, and chair (also with walls).   I have a house which is about 7x8, then a roof space above that; about half the area. I could put furniture up there too, but will anyone move in?


Why I can't update any apps and it keeps on saying that I have insufficient storage but I think its not the problem because I have storage. So what should I do?

After one of the latest updates (not sure if it was the last one or a previous one) of the Google Play app, I am having an error trying to update a large app (42MB). It says:     Error Downloading . There is insufficient space on the device.   My device is a Samsung P1000 running Froyo. It's rooted, but the error was there before rooting it.  A quick Google search showed several Samsung users having the same problem (the app in question that was giving me the headache is Smurf's village). Some said that removing the updates to the Android Market (Google Play) app would fix it, but to me it was of no avail.  I also tried the procedure in  to no avail.  Now I am stuck with a prehistoric version of the Market (that works on small apps) and still cannot update Smurf's Village or install big apps. How can I fix this?  EDIT: device has over 2GB of internal SD storage, 27GB of external SD card, so space is not an issue.


$WARNING:$ I am not a mathematician and I am asking this out of my curiousity. This question may have inappropriate tag. $BACKGROUND:$ I have tried many things to find the value of $(1/2)^{(1/3)^{(1/4)^{...}}}$ At last the only thing I could do is to approximate the expression in wolfram alpha and it seemed that this thing does converge (But I'm not sure). $QUESTION:$ If there is any closed form please help me derive it.

Prove that the sequence of general term $(\frac 12)^{(\frac 13)^{(\frac 14)^{...\frac 1n}}}$ is convergent. the three dots are antidiagonal of course :) My try was to compare it with some easier one like the power tower of $\frac 12$. I conjectured with wolframalpha that it can be divided to two subsequences which seem to be adjacent but i'm finding it hard to prove it Can anyone give some hints.


I am using Texmaker for my paper and I encounter a problem here and hope somebody can help me.    As you can see here, the titles are some in Italics and some are not. What cause this anyway? I don't use cite btw, only footnote.  \begin{thebibliography}{99}  \bibitem[Monopolkommision (1988)]{monopol1988} Monopolkommision (1988): \em{Siebentes Hauptgutachten der Monopolkommission 1986/1987}, In: Deutscher Bundestag Online, 19.07.1988 (http://dipbt.bundestag.de/doc/btd/11/026/1102677.pdf vom 16.08.2016). \bibitem[Monopolkommision (1992)]{monopol1992} Monopolkommision (1992): \em{Neuntes Hauptgutachten der Monopolkommission 1990/1991} (http://dipbt.bundestag.de/doc/btd/12/030/1203031.pdf vom 16.08.2016). \bibitem[Monopolkommision (2016)]{monopol2016} Monopolkommision (2016): \em{Wettbewerb 2016: Einundzwanzigstes Hauptgutachten der Monopolkommission gemäß § 44 Abs. 1 Satz 1 GWB} (http://www.monopolkommission.de/index.php/de/gutachten/hauptgutachten/liste-hauptgutachten vom 21.09.2016).  \end{thebibliography}   what is wrong here? these are the packages i used.  \documentclass[oneside,12pt,german , a4paper]{article} \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \usepackage[backend=biber,style=authoryear]{biblatex} \usepackage{geometry} \usepackage[graphicx]{realboxes} \usepackage{lmodern} \usepackage{setspace} \usepackage{caption} \usepackage{eurosym} \usepackage{import} \usepackage{float} \usepackage{biblatex} \usepackage{pdflscape} \usepackage{multirow} \usepackage{pbox} \usepackage{filecontents} %\usepackage{acro} \usepackage[printonlyused]{acronym} \usepackage[bottom]{footmisc} \geometry{  a4paper,  total={210mm,297mm},  left=45mm,  right=15mm,  top=25mm,  bottom=15mm,  }  \graphicspath{ {images/} } \onehalfspacing \captionsetup{justification=raggedright,singlelinecheck=false} \nocite{*}   I did have some renewcommand, but I think this is not the cause.  \makeatletter %\renewcommand{\bibname}{Literaturen} \renewcommand{\contentsname}{Inhalt} %\renewcommand{\acronymname}{Abkürzungsverzeichnis} \renewcommand{\figurename}{\textbf{Abbildung}} \renewcommand\listfigurename{Abbildungsverzeichnis} \renewcommand\listtablename{Tabellenverzeichnis} \renewcommand\@biblabel[1]{} \renewcommand\footnotesize{%    \@setfontsize\footnotesize\@ixpt{10}%    \abovedisplayskip 8\p@ \@plus2\p@ \@minus4\p@    \abovedisplayshortskip \z@ \@plus\p@    \belowdisplayshortskip 4\p@ \@plus2\p@ \@minus2\p@    \def\@listi{\leftmargin\leftmargini                \topsep 4\p@ \@plus2\p@ \@minus2\p@                \parsep 2\p@ \@plus\p@ \@minus\p@                \itemsep \parsep}%    \belowdisplayskip \abovedisplayskip } \makeatother   I think I post in the wrong website since nobody answer me on Stackoverflow. Anyway thank you for the help.

What is the difference between \emph{...} and {\em ...}?  When to use each of them?


I have seen code for replacing a broken image with javascript using onerror, but I have a situation where I'm not sure what image is going to be available for a replacement, so I need to do multiple checks and I'm not sure how... Here's an example of what I need...    If that image isn't available, I need to check a different location for an image.  that location will be...    If that image isn't available, I need to check,    and finally, if that image isn't available, I use my default image that I know is always available    javascript only please, no jquery

I have a web page that includes a bunch of images. Sometimes the image isn't available, so a broken image is displayed in the client's browser.  How do I use jQuery to get the set of images, filter it to broken images then replace the src?    --I thought it would be easier to do this with jQuery, but it turned out much easier to just use a pure JavaScript solution, that is, the one provided by Prestaul.


Show that for all $u,v \in \mathbb{R}, u>v$ if and only if $u^3 > v^3$.  Hi, just wondering how everyone thinks best to prove this? I was thinking of using cases but not sure!  Thank you!

So I took a calculus course and my first homework has this one. I am stuck on this one for 2 days straight. Please help me; I will appreciate some hints.   So far we learned the axioms of a field and the axioms for inequality (trichotomy, transitivity, etc.) Do I actually need to divide it into cases where both $x,y$ are with the same sign and another case where they are with different signs?  Is there an elegant and short way for this?


In order to get approved for most credit cards, you need to have a good credit score. But why do the credit card companies want people with good credit scores (which indicate that you're more likely to pay bills on time), when they make the most money off of charging interest on late payments?  I can think of two possible reasons, but neither seems like a complete explanation...  1) They don't want to run the risk of people completely defaulting on debt - But it seems like the easy answer here is to approve people with medium credit scores (i.e., people who generally pay bills late, but won't default)  2) They need cash on hand to supply credit - But it seems like they could get this by having a balance of people who pay on time, with those who don't.  I understand that credit card companies can still make money in other ways, but my question is different: why do they actively seek people who pay their bills on time (as evidence by requiring good credit scores to get approved for a card), instead of they opposite?

How does a credit card company make any money off of me using their card if there are no fees associated with the card (I don't pay any extra) and I pay off my balance on time every month (so I don't pay any fees ever for this either).  Are they just banking on the fact that many people don't do this and end up owing them money?


I need to check the current date with the date we enter in the input element.  Html code:  <input type="date" name="date" id="date>   I can get the today's date by the following code in javascript:  function todayDate() {    var today = new Date();    var dd = String(today.getDate()).padStart(2, '0');    var mm = String(today.getMonth() + 1).padStart(2, '0');     var yyyy = today.getFullYear();    let date=dd+'/'+mm+'/'+yyyy;    return date;  }   Now how to check the input date with the current date?

Can someone suggest a way to compare the values of two dates greater than, less than, and not in the past using JavaScript? The values will be coming from text boxes.


If I change the password for the root user is that going to automatically change the password for the user account?   I found this link for root:    How do I change the user account password?


I've set up proftpd to use ssl/tls. Trying to connect I get an 'Illegal PORT command'  Finding Host xxx.nl ... Connecting to xxx.xxx.xxx.xxx:21 Connected to xxx.xxx.xxx.xxx:21 in 0.018001 seconds, Waiting for Server  Response Initializing SSL Session ... 220 FTP Server ready. AUTH TLS 234 AUTH TLS successful SSL session NOT set for reuse SSL Session Started. Host type (1): AUTO USER xxx 331 Password required for xxx PASS (hidden) 230 User xxx logged in SYST 215 UNIX Type: L8 Host type (2): Unix (Standard) PBSZ 0 200 PBSZ 0 successful PROT P 200 Protection set to Private PWD 257 "/" is the current directory CWD /var/www/html/ 250 CWD command successful PWD257 "/var/www/html/" is the current directory TYPE A 200 Type set to A PORT 192,168,192,14,211,181 500 Illegal PORT command Port failed 500 Illegal PORT command PASV 227 Entering Passive Mode (xxx,xxx,xxx,xxx,160,151). connecting data channel to xxx.xxx.xxx.xxx:160,151(41111) Failed to connect data channel to xxx.xxx.xxx.xxx:160,151(41111)   iptables:  Chain INPUT (policy ACCEPT) target     prot opt source               destination ACCEPT     icmp --  anywhere             anywhere            /* 000 accept all icmp */ ACCEPT     all  --  anywhere             anywhere            /* 001 accept all to lo interface */ REJECT     all  --  anywhere             loopback/8          /* 002 reject local traffic not on loopback interface */ reject-with icmp-port-unreachable ACCEPT     all  --  anywhere             anywhere            /* 003 accept all to eth1 interface */ ACCEPT     all  --  anywhere             anywhere            /* 004 accept related established rules */ state RELATED,ESTABLISHED ACCEPT     tcp  --  anywhere             anywhere            multiport ports ftp /* 021 allow ftp. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports ssh /* 022 allow ssh. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports smtp /* 025 allow smtp. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports pharos /* 051 allow rundeck. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports 8140 /* 814 allow puppetserver. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports http /* 080 allow http. */ ACCEPT     tcp  --  anywhere             anywhere            multiport ports https /* 443 allow https. */ DROP       all  --  anywhere             anywhere            /* 999 drop all */  Chain FORWARD (policy ACCEPT) target     prot opt source               destination  Chain OUTPUT (policy ACCEPT) target     prot opt source               destination   Connecting via normal ftp works just fine...   I'm using WS_FTP with ftp-authssl//xxx.nl/.... I tried several other connection options, ports, etc. But all give the same error. Althoiugh it seems that sometimes a first directory listing is shown (but that might be caching of WS_FTP)


Is there any general method by which we can find the set of all automorphisms of a group? if not then find all automorphisms of a group with the help of an example.

How exactly would you find all the automorphism of something like $Z_8$ or $U(8)$?    I read that there are $4$ automorphisms of $Z_8$, but how did they come about it?  Please explain this as if talking to a beginner. Thanks


i have to test if the cvs file exists and could be downloaded from a webapp, So in the download link element, i see this :  <a class="" target="_blank" download="Myfile(2014-07-01 2014-07-31).csv" href="blob:de3889b8-23d4-4776-bn8f-68f34911fad9">   it is encoded in Base64 using java.  How can i decode the content of href in order to download the csv file? Thank you

I have an image that is Base64 encoded. What is the best way to decode that in Java? Hopefully using only the libraries included with Sun Java 6.


systems can be defined and redefined and so the meaning of what an internal or an external force is also changes:  I think im wrong here: if then we consider planet earth a system, all the things ( cars moving etc ) that happen in this system, are they internal forces,?  if there is a change in momenta inside the system, then it is caused by a force. no doubt. internal forces. why then is it said that an internal force cant cause a change in momentum?  what i think: the system's momentum as a whole doesnt change .. but i cant go anywhere from that fact for some reason. im stuck

For the earth sun system, the force of gravitation is an internal force ( forces* a newtons third law pair)  and this INTERNAL force  is causing the earth to accelerate. . it is providing the necessary centripetal force.   Reasoning behind the question:  centripetal forces dont do any work and hence dont cause a change in mechanical energy, dont cause a change in kinetic energy therefore and dont cause a change in velocity.   QUESTION question 1) but the earth is undergoing a change in velocity?  so, is the the gravitational force on the earth an external force? but ive considered our system containing the sun too. shouldn't that be an internal force then?  2) in the earth sun system if for simplicity we call the earth's movement uniform circular motion, is momentum conserved in this system? how?  i suppose ive mixed up too many things


I have the following Enum:  public enum ItemType {    Foo =0,    Bar =1 }   and then a string that is passed to a method in lowercase.  How can I compare the string to my enum and return the enum.  public ItemType Method(string value) {    ///compare string to enum here and return Enum }    and the method receives the value as parameter like this (notice the lowercase)  string value = "foo";  /// or value ="bar"  ItemType type = Method(value)

What's the best way to convert a string to an enumeration value in C#? I have an HTML select tag containing the values of an enumeration. When the page is posted, I want to pick up the value (which will be in the form of a string) and convert it to the corresponding enumeration value. In an ideal world, I could do something like this: StatusEnum MyStatus = StatusEnum.Parse("Active");  but that isn't a valid code.


How do you keep the one very experienced player from offering advice during  encounters, combat, etc.? Hes a great player, knows his stuff extremely well, but can't seem to keep his mouth shut, even when his character is not present for meetings, combat, etc.  I have found giving him gummy bears works to keep his mouth occupied, but would like other options.

I am the DM for a group of players, 4 of which are very new to the game, and one of which is a very experienced player.   I have run into a problem now where the experienced player is effectively trying to play everyone else's characters (telling them what they should be doing, getting frustrated when they don't do what he says, etc..). This player is also a massive rules lawyer, making it rather frustrating for me. He argues against rules he dislikes, and tries to get me to change rules unfavorable to him. Example: He got into a 10 minute argument trying to get me to change the damage vulnerabilities of animated rugs to include fire because he thought they should, and he was a fire elemental at the time.   Additionally, he continues to play optimized characters that make it difficult to form encounters of any kind, because if an encounter works against him, he complains about how I am "specifically trying to nerf his character because he knows how to play." Specifically, the optimized character issue is an Aarakokra druid. Flies above you, turns into an elephant. He complains when I put anything that can hit him when he's in air.   I have tried to talk to him about it, but he won't back down from his position, and I'm not sure what to do. I would respectfully ask him to leave, but I DM at an after-school intramural (high school) and I am unable to make him leave, because of the nature of school clubs. We are both students. We have a faculty advisor, but they don't understand the issue.  And everyone agreed to let me DM at the beginning because I was the only one with DM experience. We have run and enjoyed one campaign together already.  Anyone dealt with a similar situation and had a solution work for them?


While downloading MiKTeX downloading was not achieved and I get:  "C:\Program Files (x86)\New folder (2)\miktex/bin\initexmf.exe" --update-fndb --admin --log-file="C:\Program Files (x86)\New folder (2)\miktex\config\uninst.log" --verbose: Skipping user root directory (C:\Users\Souhayla\AppData\Roaming\MiKTeX\2.9)... Skipping user root directory (C:\Users\Souhayla\AppData\Local\MiKTeX\2.9)... Creating fndb for common root directory (C:\ProgramData\MiKTeX\2.9)... Creating fndb for common root directory ("C:\Program Files (x86)\New folder (2)")... "C:\Program Files (x86)\New folder (2)\miktex/bin\initexmf.exe" --force --mklinks --admin --log-file="C:\Program Files (x86)\New folder (2)\miktex\config\uninst.log" --verbose: Making format links... Making script links...  Sorry, but "MiKTeX Configuration Utility" did not succeed.  The log file hopefully contains the information to get MiKTeX going again:    C:/Users/Souhayla/AppData/Local/MiKTeX/2.9/miktex/log/initexmf.log  You may want to visit the MiKTeX project page (http://miktex.org), if you need help.  An error occurred:   source file: Libraries\MiKTeX\Core\Process.cpp   source line: 308   message: The operation failed for some reason.   info: C:\Program Files (x86)\New folder (2)\miktex/bin\initexmf.exe   What should I do?

I installed a new hard drive on my computer this summer and I'm trying to install MiKTeX on it now. There were no problems when I was using my old hard drive. My OS is Windows 8.1. I'm trying to compile the following very basic file with pdfLaTeX:  \documentclass{article} \begin{document}   hi   \end{document}   Here's the first error I get:  Sorry, but "MiKTeX Configuration Utility" did not succeed.     The log file hopefully contains the information to get MiKTeX going again:   C:/Users/Tyler/AppData/Local/MiKTeX/2.9/miktex/log/initexmf.log  You may want to visit the MiKTeX project page (http://miktex.org), if you need help.   With the following errors in the log:  2015-09-03 22:23:51,625-0400 INFO  initexmf - starting: MiKTeX Configuration Utility 2.9.5700 (MiKTeX 2.9 64-bit)    2015-09-03 22:23:51,631-0400 FATAL initexmf - Windows API error 32: The process cannot access the file because it is being used by another process. 2015-09-03 22:23:51,631-0400 FATAL initexmf - Info: C:\Users\Tyler\AppData\Local\MiKTeX\2.9\miktex/data/le\1e0c0e04cb3be262fbb8e6e7ace14b67.fndb 2015-09-03 22:23:51,631-0400 FATAL initexmf - Source: Libraries\MiKTeX\Core\win\winFile.cpp 2015-09-03 22:23:51,631-0400 FATAL initexmf - Line: 520   The second error:  Sorry, but C:\Program Files\MiKTeX 2.9\miktex\bin\x64\miktex-pdftex.exe did not succeed. The log file hopefully contains the information to get MiKTeX going again:   C:/Users/Tyler/AppData/Local/MiKTeX/2.9/miktex/log/miktex-pdftex.log  You may want to visit the MiKTeX project page (http://miktex.org), if you need help.   with the following errors in the log:  2015-09-03 22:16:18,715-0400 INFO  miktex-pdftex - running 'initexmf --quiet --update-fndb' to refresh the file name database 2015-09-03 22:16:18,746-0400 FATAL miktex-pdftex - The operation failed for some reason. 2015-09-03 22:16:18,746-0400 FATAL miktex-pdftex - Info: C:\Program Files\MiKTeX 2.9\miktex\bin\x64\initexmf.exe 2015-09-03 22:16:18,746-0400 FATAL miktex-pdftex - Source: Libraries\MiKTeX\Core\Process.cpp 2015-09-03 22:16:18,746-0400 FATAL miktex-pdftex - Line: 290   Things I've tried:   Uninstalling and reinstalling MiKTeX Downloading all packages whose name starts with miktex (which is a solution that worked for someone else in a different thread) Having nothing open but TeXworks when trying to compile Looking for processes that may be related to MiKTeX in the task manager (I didn't find any)   How can I stop these errors? I apologize if my formatting is bad; this is my first stackexchange question. Thank you for your help.


I need help on how to show that for each positive integer $n$, $2009^n − 209^n − 839^n + 92^n$ is divisible by $117$.   I have tried divisible rule but couldn't come up with anything meaningful.  Any help?


In how many ways can $5$ rings of different types be worn on $4$ fingers?   According to me,first finger have $5$ ways,second finger have $4$ ways, third finger have $3$ ways and last finger have $2$ ways.  Therefore there are $5 \cdot 4 \cdot 3 \cdot 2 = 120$ arrangements.  But in my textbook it's answer is $4^5$.

In how many ways $5$ different rings can be worn on $4$ fingers ?   Although these is similar question here   But I want to answer it in different way which is like take $4$ fingers like $a,b,c,d$. Now $a$ can be filled in $5$ ways and so are others. So total ways are $5^4$ but answer is $4^5$. What is wrong in my reasoning? Which cases have I left out?


Let $f:[0,1]\to \mathbb{R}$ be a continous function. Show that $\displaystyle\lim_{n\to \infty} \Pi_{k=1}^n  (1+ \frac 1n f\big( \frac kn\big))=e^{\int_0^1 f(x) dx}   $ My attempt :- The exponential on RHS compels me to take ln both sides but keeping in mind the terms could be negative , I tried the following . Since the function is continous on $[0,1]$ , there  exist $N\in \mathbb{N}$ such that $|f(x) | \lt N, \forall x \in [0,1]$ Now let $n\gt N$ Then $1+\frac 1n f\big( \frac k n\big) \gt 0 $ for $1 \le k \le n$ Let $P_n =\Pi_{k=1}^n  (1+ \frac 1n f\big( \frac kn\big))$ be the partial product sequence for $n\gt N$ Then, taking $\ln $ both sides, and using the fact $e^x \ge 1+x, \forall x \in \mathbb{R}$ $\ln (P_n)=\sum_{k=1}^n\ln (1+ \frac 1n f\big( \frac kn\big))\le \sum_{k=1}^n \frac 1n f(\frac kn )$ $\lim \sup  (\ln (P_n)) \le \int_0^1 f(x)dx$ How do I show $\lim\inf (\ln (P_n))\ge \int_0^1 f(x) dx$ ? Pleae help. Thanks for your time.

Given that $f:[0,1]\to \Bbb{R}$ is a continuous function, I need to show that $$\lim_{n \to \infty}\prod_{k=1}^{n}\left(1+\frac{1}{n}f\left(\frac{k}{n}\right)\right)=e^{\int_0^1f(x)dx}$$  Writing $$y=\lim_{n \to \infty}\prod_{k=1}^{n}\left(1+\frac{1}{n}f\left(\frac{k}{n}\right)\right)$$ and taking the logarithm of both sides and interchanging limit and logarithm(since $f$ is continuous), I get $$\log y = \lim_{n\to \infty}\sum_{k=1}^{n}\log\left(1+\frac{1}{n}f\left(\frac{k}{n}\right)\right)$$ Now I know that the limit of the Riemann sum $\lim_{n\to \infty}\sum_{k=1}^{n}\frac{b-a}{n}f\left(a+\frac{(b-a)}{n}k\right)=\int_a^bf(x)dx$. However if I want it to read $\int_0^1f(x)dx$ in the given problem, I would need the term inside the summation to read $\frac{1}{n}f\left(\frac{k}{n}\right)$. The way to do this it would seem is to take the series expansion of $\log(1+x)$ and ignoring the $x^2$ and higher order terms. Is it justifiable to do so?


I have been having trouble understanding the translation of a graph. I understand the 'rule in the sense that the '$+$' shifts to the left and the '$-$' to the right when dealing with something like e.g. $f(x + 2) = f(x)$.  In the book I am using it has written that if $g(x) = f(x-c)$, where $c > 0$ then the value of $g$ at $x$ is the same as the value of $f$ at $x-c$.  So ...if $c = 2$ and my function for $g$ was $g(x) = x^2$ and I put in $x=3$ I'd get $9$. For $f(x-c)$ I don't quite understand this part. Am I wanting to put in the same $x$ (i.e. $x = 3$) which would give me $f(3-1) = f(1) = g(3) = 9$. When I do this it seems to work against how I thought it would go. To me this implies that in $g(x)$ when I input $3$ for $x$ I'd get a $y$ value of $9$. Then when I input $x=3$ in the function for '$f$' I'd end up with $f(1)$ provides me with $9$. It seems $g(1)$ is going back $2$ spaces to the left when compared to $f(3)$ in order to get the answer $9$ (based on $3-1 =2 $, from within the functions respective brackets)  Clearly I misunderstand something here.....

I always find myself wanting for a clear explanation (to a college algebra student) for the fact that horizontal transformations of graphs work in the opposite way that one might expect.  For example, $f(x+1)$ is a horizontal shift to the left (a shift toward the negative side of the $x$-axis), whereas a cursory glance would cause one to suspect that adding a positive amount should shift in the positive direction. Similarly, $f(2x)$ causes the graph to shrink horizontally, not expand.  I generally explain this by saying $x$ is getting a "head start". For example, suppose $f(x)$ has a root at $x = 5$. The graph of $f(x+1)$ is getting a unit for free, and so we only need $x = 4$ to get the same output before as before (i.e. a root). Thus, the root that used to be at $x=5$ is now at $x=4$, which is a shift to the left.  My explanation seems to help some students and mystify others. I was hoping someone else in the community had an enlightening way to explain these phenomena. Again, I emphasize that the purpose is to strengthen the student's intuition; a rigorous algebraic approach is not what I'm looking for.


My wheels are slightly out of true, about 1.5 mm at worst part. It doesn't bother me when riding and I don't feel it, but will this hurt or damage the wheel if I keep going on, or should I keep going until it starts bothering me?

I understand that wheels should be trued for efficiency. Are there any safety risks (or risk  of damaging the bike) in using untrued wheels?  Are the risks different between wheels untrued left-right and up-down?  My question is motivated by the following fact: I have an up-down untrued wheel and not much time to take it to the shop, should I keep using the bike?


If $A = u\cdot u^T$ where $0 \neq u \in \mathbb{R}^n$ , then    find the eigenvalues of $A$ and show that $A$ is diagonalizable.   I mean how to find eigenvalues of $A$?

Given a column vector $v$ in $\mathbb{R}^n$, what are the eigenvalues of matrix $vv^T$ and associated eigenvectors?  PS: not homework even though it may look like so.


i want to know that if i upgrade my system from 13.04 to 13.10.Is there any chance of data loss(music,documents,video etc.) after upgradation?

I am planning to upgrade from 8.10 to 10.04. But I am wondering whether there will be data loss during the upgrade.  For example:   Will the applications that I have installed on 8.10 still be there after upgrade? Will the settings of application such as the bookmarks for Firefox and for Google Chrome be preserved? Will all the personal files under my home directory be preserved?   Is there anything else I need to know about upgrading?


I just downloaded the file with the extension ".iso". I click on it and nothing happens. I opened up VirtualBox to try and use it and I get an error message about a kernel module. (Kernel driver not installed (rc=-1908)). What do I do now?

I tried to use my Virtual Box and this is the error I received - (I just updated to the new Ubuntu also) and I am VERY new at this Linux OS.     Kernel driver not installed (rc=-1908)      The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or   there is a permission problem with /dev/vboxdrv. Please reinstall the   kernel module by executing      '/etc/init.d/vboxdrv setup'      as root. Users of Ubuntu, Fedora or Mandriva should install the DKMS   package first. This package keeps track of Linux kernel changes and   recompiles the vboxdrv kernel module if necessary.


Could anyone give me some references for mathematicians (coordinates free notation, formalism of fiber bundles etc.) about tetrads, Palatini-Cartan theory, stuff about formulation of GR with tetrads?  Please no books with explicit coordinates notation.

I'm still self-learning general relativity. I have been a huge fan of  on GR, black holes and cosmology. He goes through GR in pretty much full tetrad formalism. The reason he wants to do that is because some of the physics becomes much easier to understand in local tetrad frame, where everything just follows special relativity. That's the reason people working with particle physics in GR are interested in working with tetrads, I suppose. While I think Andrew Hamilton's notes are the most amazing thing in this world, I find myself sometimes wanting to read more books on tetrads and particle physics. That's why I'd like to ask if anyone knows more fairly comprehensive sources to learn about tetrads and particle physics in GR. One thing I sometimes find is lacking in the above notes is exercises / example calculations (only in some chapters). This is why I'd especially appreciate resources with many exercises to master the basics. I'd like to think my background in GR is not too bad right now, but I still find myself struggling with quantum physics from time to time. Thanks a lot! Too Long Didnt Read I would like resources which have the following:  General Relativity Lots of tetrads Particle physics Exercises & applications


So I had previously installed these and now I have uninstalled them but an empty icon with their name is generated and I want to remove it.  I tried right clicking and then show details but in software centre it is showing as uninstalled.  Cannot add screen cast because of size limit   Names of apps: Coolreader3, Deadbeef

When searching for "Skype" I always see these 2 entries.  There is this duplicate blank Skype icon. Both of them seem to run Skype in the same way.    But I've checked both /usr/share/applications, and ~/.local/share/applications, and can't find the extra icon so I can delete it.    Also as described , sometimes similar ghost icons are present even after removing associated applications.


Let $a_1,a_2,a_3,...,a_n$ be the sequence of Fibonacci numbers.  Then we are required to prove by induction that $$a_{n+1}^2=a_n \cdot a_{n+2} + (-1)^n$$  My Attempt:  Initially putting a few values like $n=1,2 \: \text{or}\ 3$ makes it certain that we can move ahead.  Following the conventional way we can assume that the proposition holds true for some $k$ s.t.$$a_{k+1}^2=a_k \cdot a_{k+2} + (-1)^k  \tag1$$  To prove that the proposition holds for all values of $n$, we need to prove for the same for $n=k+1$ too.  In short we need to prove that: $$a_{k+2}^2=a_{k+1} \cdot a_{k+3} + (-1)^{k+1}  \tag2$$  We know that   $$ a_{k+2}^2=(a_{k+3}-a_{k+1})^2$$ $$\Rightarrow a_{k+2}^2=a_{k+3}^2+a_{k+1}^2-2\cdot a_{k+3}\cdot a_{k+1}$$ $$\Rightarrow a_{k+2}^2=a_{k+3}^2+a_k \cdot a_{k+2} + (-1)^k-2\cdot a_{k+3}\cdot a_{k+1}$$ $$\Rightarrow a_{k+2}^2=a_{k+3}[a_{k+3}- 2\cdot a_{k+1}]+a_k \cdot a_{k+2} + (-1)^k \tag{*}$$  It is easy to see that $$a_{k+3}-a_{k+1}=a_{k+2} \tag3$$  And $$a_{k+2}-a_{k+1}=a_{k} \tag4$$  Adding equation $3$ and $4$, we get$$a_{k+3}-2a_{k+1}=a_{k} \tag5$$  Putting eq$(5)$ in eq$(*)$   $$a_{k+2}^2=a_{k+3}[a_k]+a_k \cdot a_{k+2} + (-1)^k $$ $$\Rightarrow a_{k+2}^2=a_k[a_{k+3}+a_{k+2}]+(-1)^k $$ $$\Rightarrow a_{k+2}^2=a_k(a_{k+4})+(-1)^k$$  This I indeed completely different from something that I wanted to prove. Is there any way to get ahead of this or is there something wrong with what I have done?

Consider this Fibonacci equation: $$f_{n+1}^2 - f_nf_{n+2}$$  The problem asked to write a program with given n, output the the result of this equation. I could use the formula  $$f_n = \frac{(1+\sqrt{5})^n - ( 1 - \sqrt{5} )^n}{2^n\sqrt{5}}$$  However, from mathworld, I found this formula Cassini's identity  $$f_{n-1}f_{n+1} - f_{n}^2 = (-1)^n$$  So, I decided to play around with the equation above, and I have:  $$ \text{Let } x = n + 1 $$ $$ \text{then the equation above becomes } f_x^2 - f_{x-1}f_{x+1} $$ $$ \Rightarrow -( f_{x-1}f_{x+1}  - f_x^2 ) = -1(-1)^x = (-1)^{x+1} = (-1)^{n+1+1} = (-1)^{n+2}$$  So this equation either is 1 or -1. Am I in the right track?     Thanks, Chan


I'm trying to show that a continuous function $f:(a,b) \to \mathbb{R}$ with the mid-point convexity property is convex.  Midpoint convexity is $f((x+y)/2) \leq \frac{1}{2}f(x) + \frac{1}{2} f(y)$. Convexity is $f(tx + (1-t)y) \leq tf(x) + (1-t)f(y)$ for all $t \in [0,1]$.  Starting with $f((x_1 + x_2)/2) \leq \frac{1}{2} f(x_1) + \frac{1}{2} f(x_2)$, I could show   $$f((x_1 + x_2+ x_3 + x_4)/4) \leq \frac{1}{4} f(x_1) + \frac{1}{4} f(x_2)+ \frac{1}{4} f(x_3)+ \frac{1}{4} f(x_4)$$  Using induction I get for all $n$  $$f\left(2^{-n}\sum_{j=1}^{2^n}x_j\right) \leq 2^{-n}\sum_{j=1}^{2^n}f(x_j). $$  I can see that continuity lets me take a limit inside $f()$, but I'm not sure how to continue to prove the general property.

Given that $$f\left(\frac{x+y}{2}\right)\leqslant \frac{f(x)+f(y)}{2}~,$$ how can I show that $f$ is convex. Thanks.      Edit: I'm sorry for all the confusion. $f$ is assumed to be continuous on an interval $(a,b)$.


In tex environment, when I try to use the verbatim function using verbatim packages, sometimes the longer text in the line tend to be cut off. How can I resize the text to fit into the line or automatically extend the text to the next line so as to retain all the text. For example I have the following text:      \begin{verbatim}         C **  RAINCVT   =CONVERTS RAIN TO UNITS OF M/SEC , inch/day=0.0254m/86400s=2.94E-7m/s, inch/h=7.05556E-6m/s C **  EVAPCVT   =CONVERTS EVAP TO UNITS OF M/SEC, IF EVAPCVT<0 EVAP IS INTERNALLY COMPUTED C **  SOLRCVT   =CONVERTS SOLAR SW RADIATION TO JOULES/S/SQ METER (Watts/m^2)     \end{verbatim}   In my output the first line doesn't show all the text. I would also appreciate if someone could tell how to limit the floating verbatim ? In tables using the label [h] at the end would fix the position of the table which doesn't seem to work on verbatim.

I want to generate a PDF of user-submitted text using LaTeX. To handle crazy user input, I first thought about using the verbatim package, but of course it doesn't break up too long lines. Is there some package that works similar to verbatim (i.e., accept any input) but formats the text nicely?


It’s been spreading for a while now and... I don’t know what to do. How can I cleanse it in the most efficient, easiest way?

After the Wall of Flesh, the Hallow appears and Corruption/Crimson spreads even faster.   Corruption/Crimson spreads through everything   Except Hallow  Hallow spreads through everything   Except mud (jungle) Except synthetic blocks like gray-brick  The results of Hallow and Corruption meeting are unpredictable   How can I stop them both permanently and effectively from taking over the world, considering both the top layer and underground?  (Eg, simply placing gray brick on top of the surface won't stop the underground spread?)  And, is it worth the effort?


I currently have a laptop w. a 2tb internal hard drive & Windows 10 installed on it.  For coding reasons, I would like to run Ubuntu from a USB drive if I needed to but still retain my Windows hard disk and not modify it in any way.  I already made a USB stick with an ISO Ubuntu 17.04 image, but anything I do on it is not retained once I shut down the PC; therefore, I suspect I need to fully install it to a storage device, but I don't want to run the risk of accidentally wiping my internal HDD... how would I go about doing this?  Any help is appreciated; thanks, in advance.

If you are hurrying to reply, System → Administration → StartUp Disk Creator -- no, that's not what I'm talking about.   I want to try Ubuntu 11.04's Unity without touching my existing Ubuntu install.  To do this, I need to install the nVidia drivers first (sigh).  To do this, I need changes to persist a reboot.  To do this, I need to really install Ubuntu on a USB key.  How do you do that?    What I tried   I tried to make a USB key from , then boot from it, then choose "Install Ubuntu." The installer refused to install to the installation media itself. I tried, from my installed copy of Ubuntu:  sudo kvm /dev/sdb --cdrom .cache/testdrive/iso/ubuntu_natty-desktop-i386.iso   ...but the installer didn't detect the disk properly.


I did some research and found that an earth-mass black hole, has theoretical mean density inside the Schwarzschild radius about 4•10^17 kg/m³. This is well within density of neutron stars which are almost entirely made of neutrons. So what kind of matter makes them? Is it the elementary particles or heavier elements?  PS: I found one very complicated answer on Reddit but I'm looking for a more elementary one, if possible at all. Thanks

Imagine a black hole originally formed from, for example, Rubidium atoms. On the other hand, one made from, for example, Helium atoms. Will it be there any difference between the two? Or perhaps once formed it all turns into the same type of matter?  Can the "composition" of the matter-energy in the black hole be inferred somehow?  Could one say that "black hole substance" is a distinct form or state of matter different from other forms or states of matter?


What is the point of the concept of surjective or onto functions if you can just restrict the co-domain of your function to its image? Injectivity or 1-to-1ness is actually the defining property of bijections (sometimes called 1-to-1 correspondences), while all the question of surjectivity does is derail the argument into checking whether the image equals the co-domain.  Am I wrong in thinking this? What am I missing? Only situation where this concept could be marginally useful that I could think of would be some function for which it is easier to find an element of the co-domain for which no pre-image exists than to actually find the image itself.

So as far as I understand, a function $f\colon A \to B$ is surjective if and only if for every $b\in B$ there exists $a\in A$ such that $f(a) = b$.  My question is when is this actually relevant? Couldn't you arbitrarily define the set $B$ so that any elements never "used" are removed from the set, leaving you with a surjective function?


Food and equipment becomes or become expensive. I am not sure if I should use become or becomes in this sentence.

I was surfing the internet the other day when I found this phrase: Instead your precious time and attention is wasted. To my ears, it sounds wrong. But I'm not a native English speaker, so I consulted with a number of them, and some of them said that it was "is" because the adjective modifies only the noun "time" and not "attention". Others said it "is" because that's just how it is. But I still believe it should be "are". Any help is appreciated.


Is there a way to prevent the X-Forwarded-For from being spoofed in haproxy?  i.e. Can I rename that header to something else? Or is there another way to forward on the correct IP address of the client?

Yesterday we got hit by a DDoS attack reaching our webserver backends (apache2). The frontend consists of haproxy loadbalancing connections to the webservers. On access.log of apache we saw thousands of requests from two ips and after a couple of hours we realized that those were fake/spoofed and were not the actual ips.  For clarification reasons, we did a "curl GET /" with an ip of "137.137.136.136" and indeed that's the ip (fake one) we saw in our weblogs  Now, in another cluster where we use nginx as reverse proxy, changing/crafting the X-Forwarded-For Header doesn't work. Meaning , even if you enter a random ip in the specific header nginx will still pass the correct ip to the backend webserver?  Does this has to do with haproxy? Anyone can confirm that crafted X-Forwarded-For headers can pass through haproxy? Why is this not happening in nginx ? How do you prevent this?


I've never worked out the general proof of l'Hôpital before, and am taking the opportunity to do so before I return to the soul-crushing grind of college life.   I looked in Spivak and found a fine proof of the $(x \rightarrow a$ and $f(x), g(x) \rightarrow 0)$ case; but when he went to prove the $(x \rightarrow \infty, f(x), g(x) \rightarrow 0)$ case, he made a suggestion which actually does not work. (He proposed applying l'Hôpital for the first case above to $f(1/x) / g(1/x)$ as $x \rightarrow 0$, but since he used the fact that $f(0)$ and $g(0)$ could be defined to prove the first case, his version doesn't seem to apply. Correct me if I'm wrong!)  I adapted this proof of the second case.    Theorem: Suppose that $\lim_{x \to \infty} f(x), \lim_{x \to \infty} g(x) = 0$, and $\lim_{x \to \infty} \frac{f'(x)}{g'(x)} = l$. Then $ \lim_{x \to \infty} \frac{f(x)}{g(x)} = l.$    Proof: Note as a lemma that there exists an interval $I = (c, \infty)$ on which   $g'(x) \neq 0$ $g(x) \neq 0$   (The hypothesis implies (1); to prove (2), note that every interval $(\eta, \infty)$ would otherwise have $g(\xi) = 0$, so taking any $\eta ' > \eta$, there would be $g'(x) = 0$ on $(\xi, \xi ')$, and thus on $(\eta, \infty)$, against (1).)  Fix $\epsilon > 0$. By hypothesis, $\exists M: x > M \implies |\frac{f'(x)}{g'(x)} - l| <  \frac{\epsilon}{2}$. If $M < c$, choose $M = c$ so $M \in I$.   Now pick any $y > M$. By Cauchy, $\forall x > y$ we get $($for $\mu \in (y, x))$  $$\frac{f(x) - f(y)}{g(x) - g(y)} = \frac{f'(\mu)}{g'(\mu)}.$$  But if we take $\lim_{x \to \infty}$ of both sides, we find  $$\lim_{x \to \infty}\frac{f(x) - f(y)}{g(x) - g(y)} = \frac{f(y)}{g(y)} = \lim_{x \to \infty} \frac{f'(\mu)}{g'(\mu)}. $$  We know that the RHS limit is determinate; we also know that  $$ l - \frac{\epsilon}{2} < \frac{f'(\mu)}{g'(\mu)} < l + \frac{\epsilon}{2} \implies l - \frac{\epsilon}{2} \leq \lim_{x \to \infty} \frac{f'(\mu)}{g'(\mu)} \leq l + \frac{\epsilon}{2}$$  $$\therefore l - \epsilon < \frac{f(y)}{g(y)} < l + \epsilon .$$  We have therefore furnished $M : |\frac{f(x)}{g(x)} - l| < \epsilon$ if $x > M$. This proves the theorem.    I now feel a sudden urge to begin overusing l'Hôpital! Someone, please tell me if this is correct, so I can go at it.

The following is an excerpt from Bartle and Sherbert's Introduction to Real Analysis:        Okay. I am having a little trouble following this proof. What is $c$ and why is it in $(a,b)$? What confuses me is that there is no reference to any $\delta$ nor any reference $x$ such that $0 < x - a < \delta$. They just simply write $L - \epsilon \le \frac{f(\beta)}{g(\beta)} \le L + \epsilon$ and claim that the conclusion follows. I suspect they are using $\beta$ in place of $x$, but this still doesn't account for the absence of a $\delta$ and why $\beta$ wouldn't satisfy $0 < \beta - a < \delta$.   On second thought, perhaps $\beta$ and $c$ are intended to stand for the typically used $x$ and $\delta$, respectively. It seems that what the authors have shown is that for every $\epsilon> 0$, there exists a $c > 0$ such that if $\beta$ satisfies $a < \beta \le c$, then $|\frac{f(\beta)}{g(\beta)} - L| \le \epsilon$. Even on that interpretation, why is $c$ (i.e., $\delta$) in $(a,b)$? In fact, if $a$ and $b$ are negative, this doesn't make much sense...  EDIT:  Okay. I think I follow what you, @Jack, are saying. However, there is one last thing giving me trouble. Just before equation (2), the authors claim that there exists a specific $u \in (\alpha, \beta)$ by the Cauchy Mean Value theorem such that equation (2) holds. Now, in order to validly substitute this in the inequality below (2) to obtain inequality (3), we need that that specific $u$ is in $(a,c)$, but this has not been demonstrated. All that we have is that if $u \in (a,c)$, then $L - \epsilon < \frac{f'(u)}{g'(u)} < L + \epsilon$, but how do we know that the specific $u$, guaranteed to exist by the Cauchy Mean Value theorem, falls in the interval $(a,c)$?  Also, it doesn't seem that we merely want to assume that $\beta \in (a,b)$ but that $\beta$ is arbitrary in $(a,c)$, right? Or may be it doesn't matter, since if we have "$\beta \in (a,b) \implies |\frac{f(\beta)}{g(\beta)} - L | <\epsilon$", then we would clearly have "$\beta \in (a,c) \subseteq (a,b) \implies |\frac{f(\beta)}{g(\beta)} - L | < \epsilon$". Am I thinking about this correctly?


Doing a math function of the type def.  def integral_error(integral,f):     ------stufff-------     print integral   gives something like: '<function simpsons at 0xb7370a74>'  is there a way to get just simpsons without string manipulations? ie just the function name?

In Python, how do I get a function name as a string, without calling the function?  def my_function():     pass  print get_function_name_as_string(my_function) # my_function is not in quotes   should output "my_function".  Is such function available in Python? If not, any ideas on how to implement get_function_name_as_string, in Python?


here's the code:  import sqlite3 cx = sqlite3.connect("test.db") cu = cx.cursor()  # create table 1. cu.execute("create table user_info1 (user_id text primary key,followers integer, asks integer, answers integer, goods integer)")  # create table 2 cu.execute("create table user_info2 (user_id text primary key,followers integer, asks integer, answers integer, goods integer)")   Now I'm wondering to see how many tables are in test.db:  cu.execute('.tables') # doesn't work.  cu.execute('select * from test.sqlite_master where type = "table"') # OperationalError: no such table: test.sqlite_master   The methods above doesn't work for me. Have any hint? Thanks!

For some reason I can't find a way to get the equivalents of sqlite's interactive shell commands:  .tables .dump   using the Python sqlite3 API.   Is there anything like that?


I am trying to implement  using additive ElGamal.  I am trying to run the full protocol mentioned in Section 3.4 on the following inputs:   $p = 17$ (prime) $g = 6$ (generator) $x = 5$ (private key) $k = g^x \pmod p = 6^5 \pmod{17} = 7$ (public key)   Suppose the clients inputs are 1, 2. Then $P(x) = (x-1)(x-2) = x^2-3x+2$, and therefore the coeffiecients to encrypt are $(1, -3, 2)$. I chose $y = 10$ and so the encrypted values are:   $1$ becomes $(15,12)$ $-3$ becomes $(15, 1)$ $2$  becomes $(15, 4)$.   The Server Side Input Set $S=\{1\}$ and the random value $r0$ corresponding to $\{1\}$ is $r_0=2$.    With the above problem in context, I have some questions:   What does P 0,j refer to in Step 7. Can you please give an example? In Step 8, suddenly variable i is introduced along with j. What does i, j, refer to? In Step 8, ENC() function has a ; in between. How do we interpret ENC(a;b)?


A bit over a year ago, there was . This was also referenced in  Are there any more recent publications involving Stack Overflow or Stack Exchange?  Also, what is the best way to keep informed of such work? By keeping in contact with the Stack Exchange folks directly?

As a result of  myself, the need arose to track other Stack Overflow-based research. The following is an attempt to list the academic papers mentioning Stack Overflow/Exchange or using Stack Exchange data. This also includes the works mentioned in  that started the trend, as well as two other questions on meta, , and . If you know of papers that are not listed, please edit the answer directly. I realised it might be useful to have all the BibTeX entries in a single file, so I started .


I need a faster method to find the maximum double value from a sub array.  This is how I do it now:  static double FindMax(double[] x, int startIndex, int endIndex) {     int i = startIndex;     double max = x[i++];     double value;     while(i <= endIndex)     {         value = x[i++];         if (value > max) max = value;     }     return max; }   But it is a bit slow. I need a faster method. Any tips?

Let's say I have an Array of numbers: [2,3,3,4,2,2,5,6,7,2]  What is the best way to find the minimum or maximum value in that Array?  Right now, to get the maximum, I am looping through the Array, and resetting a variable to the value if it is greater than the existing value:  var myArray:Array /* of Number */ = [2,3,3,4,2,2,5,6,7,2];  var maxValue:Number = 0;  for each (var num:Number in myArray) {     if (num > maxValue)         maxValue = num; }   This just doesn't seem like the best performing way to do this (I try to avoid loops whenever possible).


Let's suppose I have such code:  public class OuterClass{     InnerClass myInnerClass = new InnerClass();     public class InnerClass{      } } // somewhere I have created an OuterClass instance: OuterClass outerClass = new OuterClass(); // do something // ... outerClass = null;   The question: is it enough to set only the outerClass to null to avoid the memory leak? InnerClass has a reference to OuterClass, and OuterClass has a reference to InnerClass. Thus, as both of these objects have references to them, they cannot be garbage collected!

Hopefully a simple question. Take for instance a Circularly-linked list:  class ListContainer {   private listContainer next;   <..>    public void setNext(listContainer next)   {     this.next = next;   } }  class List {   private listContainer entry;   <..> }   Now since it's a circularly-linked list, when a single elemnt is added, it has a reference to itself in it's next variable. When deleting the only element in the list, entry is set to null. Is there a need to set ListContainer.next to null as well for Garbage Collector to free it's memory or does it handle such self-references automagically?


When we state that something belongs to a university, for instance requirements, we should use university's requirements or requirements of the university?  I remember learning like a thing that belongs to a non-living thing should be written as something of something instead of something's something. However, I see usage of university's something all over the place.  Pardon for the number of "something" in my questions.

My colleagues are in the design department of a given product, and when asked to add that information to the e-mail signature, they have written:     ProductName's Design   I'm objecting that the usage of the Saxon genitive there is incorrect, because the product is neither a person or animal owning anything, and Design in this context is not even a property of the product (Maybe I would admit the Saxon genitive in a context like "I think ProductName's design is not fail-safe"), but an activity.  Am I right? ^_^  update:  After reading the answers and the comments, I think the issue has been clarified a little bit. In this case ProductName is acting as an adjective qualifying Design [Department], so that's the actual reason for not using the genitive case (rather than the product being a "weak entity" unable to possess things, that is merely an stylistic rule of thumb).


I accidentally visited gist.gihub.com (note the missing t), and now that URL auto completes each time I start typing gist.…. How can I remove this URL?  I've tried removing it from my history, but that doesn't help:     (note the empty search results)

I've got a URL in Chrome "local.mysite.com" that autopopulates when I start typing "local.my" into the URL bar.  Note that this URL DOES NOT EXIST in my browser history (at chrome://history/#e=1&p=0) because it isn't a real site and therefore couldn't ever be successfully visited and therefore never shows up in my history.   The URL I want is "local.mysite.com/subdir/". That URL is 3 down in the suggested results because I keep accidentally hitting "enter" when it auto-suggests the unwanted first URL thus reinforcing its assumption that that is the one I want.   How do I get rid of the "local.mysite.com" entry in Chrome's memory?


Saw this movie/TV series the 90s, though could have been made in the 80s. It was a live action show.  Boy meets a scientist, who can open a portal to different worlds  They are being chased by an evil scientist, who wants to destroy the world. He follows them from world to world, attacking them.  Each movie (or TV series? I can't remember) has them going to a different world. In one, war has destroyed the world, and now only human like dolls exist in a carnival type world. In another, they go to a world they are are tiny, and a little baby chases them.  Boy meets with a girl from the future, who has been fighting all her life, and is surprised to hear our hero's world is peaceful. In other episode, they come to our normal world, and the girl has to pretend to a normal teenager.  In the end, we find that the   Scientist helping the hero was the bad guy, and the evil scientist they had been fighting was actually trying to save the world.    Hero saves the world, of course.

I'm looking for a 90s (or early 2000s) scifi (mini)series where a boy and old man chase a black guy in metal suit. I think they were going through different dimensions. I remember part of it, but I don't think I ever saw how it ended. I remember my friend telling me there was a twist at the end. I think they were trying to find something and he was always ahead of them..


I have a 2 files with the following:   File1.txt  A 1 B 2 C 5 Z 3  File2.txt A 4 B 7  C 10 D 11   What I would like to do is create something like   A 1 4  B 2 7 C 5 10 D - 11 Z 3 -   Is there a utility that does this? If not how Can this be done? Using a find and awk or something?


What is the Powershell equivalent of this wget command?   wget -nc -i downloadList.txt   Where      -i downloadList.txt   downloads a list of urls' in the specified file.          -nc   skips the already downloaded files.

I know I can download and install the aformentioned library (wget for Windows), but my question is this:   In Windows PowerShell, is there a native alternative to wget?  I need wget simply to retrieve a file from a given URL with HTTP GET. For instance:  wget http://www.google.com/


I left a vacuum packed chicken casserole from Whole Food  out four hours. Is it safe? The car ride from store is included in the time. Our house is not freezing nor too hot.

If I left food out of the refrigerator for some period of time, is it still safe? If I left it out too long, can I salvage it by cooking it more?


I'm a beginner, and just learn about shading following video tutorials. The first time I open the tab 'shading' everything should be white in second pic.but in my screenshot as you can see it just a mess. I reset to default settings but still the same. I'm confused, can anyone help me fix this problem?

I don't know why but now, when i go in material preview or rendered (in solid mode it works fine), my object is entirely gray, or invisible idk, because it has the same color of the background. I've been working for days on this project without having this issue, it suddenly showed up. I tried opening other old projects and suddenly they all do the same so i guess it is some blender program setting that applies for all the projects, but idk how it happened cuz i didn't change anything :/, anyone got any tips?


is there a command that kills all horses and nothing else

I use this command kill @e[type=!Player] to kill everything except for players, but does anyone know how to make it not kill tamed wolves/dogs as well as players?


I'm on minecraft, I made sure that my game mode is creative, so I don't need to hold to break blocks. Yet, I am unable to break ANYTHING. Not even DIRT. I can still place blocks, I just can't break them. Can't break any blocks in survival either..... I also cannot kill mobs. And I'm most definatly not in adventure mode! Please Help! It's been going on for weeks!

I'm playing on a Survival world with cheats on, "easy" difficulty, and at night in-game. I didn't have a sword or anything to make a sword with, and I was starving, so I switched to Creative to give myself a stack of food and a bed to set my spawn point. When I switched back to Survival, I couldn't destroy or place blocks. I'm on single player, and my Internet is fine, and I can destroy blocks still if I switch to creative. I've tried resetting the button one, and reloading the map, and it still doesn't work. I've even tried deleting everything I gave myself in Creative. This happened before on a different world and I ended up deleting it.  This only happens on this world. How do I fix it?  If I know I'm in the correct game mode, what else can cause this?  Are there different causes in multiplayer?


The first method finds the duplicate and the second removes it.  I tried the following code and it does not work. I don't understand why. to be done using two methods. When I call the methods, they do not remove the duplicates. The arraylist is unchanged. I want to remove the duplicates using two methods.   public static int find(ArrayList<String> s, int i) {      for (int j = i + 1; j < s.size(); j = j + 1) {         if (s.get(i) == s.get(j)) {             return j;         }     }      return -1; }   public static void removeDuplicates(ArrayList<String> s) {     for (int i = 0; i < s.size(); i = i + 1) {         int foundAt = (find(s, i));         if (foundAt >= 0) {             s.remove(i);         }     } }

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?