So while doing all sorts of proving and disproving statements regarding irrational numbers, I ran into this one and it quite stumped me:  Prove that $\sqrt[3]{2} + \sqrt[3]{4}$ is irrational.  I tried all the usual suspects like playing with $\sqrt[3]{2} + \sqrt[3]{4} = \frac{a}{b}$ for $a,b\in \mathbb{Z}$ , but got nowhere.  I also figured maybe I should play with it this way:  $2^\frac{1}{3} + 4^\frac{1}{3}=2^\frac{1}{3} + (2^2)^\frac{1}{3}=2^\frac{1}{3} + 2^\frac{2}{3}=2^\frac{1}{3} + 2^\frac{1}{3}\times 2^\frac{1}{3}=2^\frac{1}{3}(1+2^\frac{1}{3})$  But there I got stumped again, because while $1+2^\frac{1}{3}$ is irrational, nothing promises me that $2^\frac{1}{3} \times (1+2^\frac{1}{3})$ is irrational, and I feel like trying to go further down this road is moot.  So what am I missing (other than sleep and food)? What route should I take to  prove this? Thanks in advance!

Assume there exist some rationals $a, b$ such that $\sqrt[3]{a}, \sqrt[3]{b}$ are irrationals, but:  $$\sqrt[3]{a} + \sqrt[3]{b} = \frac{m}{n}$$  for some integers $m, n$  $$\implies \left(\sqrt[3]{a} + \sqrt[3]{b}\right)^3 = \frac{m^3}{n^3}$$  $$\implies a + b + 3 \cdot \sqrt[3]{ab}\left(\sqrt[3]{a} + \sqrt[3]{b}\right) = \frac{m^3}{n^3}$$  Since $a +b$, $\sqrt[3]{a} + \sqrt[3]{b}$ are rational, $\sqrt[3]{ab}$ must be rational as well.   For convenience let us say $\sqrt[3]{a} = p, \sqrt[3]{b} = q \implies pq$ is rational. This means, for all $i$, $p^iq^i$ is rational.  $$\implies (p + q)^2 = \frac{m^2}{n^2}$$  $$ = p^2 + q^2 + 2pq = \frac{m^2}{n^2}$$  Since $pq$ is rational, $2pq$ is rational and so is $p^2 + q^2$.  Assume, for some $i$ that $p^i + q^i$ and $p^{i-1} + q^{i-1}$ is rational.   $$\implies (p^i + q^i)(p + q) - pq(p^{i - 1} + q^{i - 1}) = p^{i+1} + q^{i+1}$$  is rational as well.  So for all $i$,  $$a^{\frac{i}{3}} + b^{\frac{i}{3}}$$  and   $$a^{\frac{i}{3}}b^{\frac{i}{3}}$$  are rational.  I know I'm really close to the answer, but it somehow just keeps slipping through my fingers.


I have just bought a DELL Laptop Vostro 3580 Intel Core I5-8265U having dedicated Ubuntu 18 already installed (customized for Dell laptop)  I'd like to ask you two questions,please:  1) Is it possible to install Windows 10 Pro 64 bit from a "regular"- off the shelf-  stick/DVD distribution as the second OS, keeping the already installed UBUNTU as the first OS and having dual boot ?  2) I believe that UBUNTU 18 is desktop version, not server version.  Is it possible to install LAMP suite on my laptop ?  I'd like to start programming in PHP and MySQL.  Thank you very much !  Best regards, Paul

I have Ubuntu on my laptop. Now I want install Windows 7 in a dual-boot. How can I do this? I can't lose my Ubuntu files, and I'm afraid that I might break . Go  for UEFI only!


I need set environment variables for Android Studio project EVERY TIME when reboot or close terminal. (Ubuntu 14.04) For setting variables I use:  export KEYSTORE_NAME=/home/anna/Documents/keys/NAME.keystore  export KEYSTORE_NAME_PASSWORD=PASSWORD export KEY_NAME_ALIAS=NAME export KEY_NAME_PASSWORD=PASSWORD   How can I set there variables forever?

What are correct places for:   Global environment variables meant to affect all users? User-specific environment variables?


I was using Ubuntu, but after updating to 14.04 LTS the Unity Desktop did not perform particularly well. So after research, I switched to Xubuntu, a recognised version of Ubuntu running the Xfce desktop environment.  Do both of these distros actually have anti-virus and anti-malware etc. built in, plus the programmable firewall, or are they just so called 'resistant' to viruses, because of supposed lack of Ubuntu specific viruses.   I have looked through many articles on Ask Ubuntu as well as other blogs, and all they seem to do is contradict.  Please help! Any help is greatly appreciated!

I thought that there was no need to scan for viruses either in Ubuntu or any Linux distros until I found virus scanner packages clamtk and klamav in Ubuntu software center yesterday.  This leads to the following questions:   How do viruses differ between Linux and Windows? How do the strategies for protection differ between Linux and Windows? Should a virus scanner package be installed on my system? If so, which would be a better option?


Aside from the very first novel I didn't find any mentioning of the broom riding classes. In the first book Malfoy taunts Harry in this class to get into the air with him, which after a series of events results in Harry ending up in the Quidditch team. However this class will never be mentioned again as far as I'm concerned throughout the books nor the movies.  Was it just a 1-2 hours long introduction? Is there no PE class at the school?

Flying lessons would be starting on Thursday — and Gryffindor and Slytherin would be learning together.   In Harry Potter and the Philosopher's Stone, Chapter Nine - The Midnight Duel Harry's first -     At three-thirty that afternoon, Harry, Ron, and the other Gryffindors hurried down the front steps onto the grounds for their first flying lesson.   (and only) flying lesson is described. During this single lesson Harry discovers that he has a tremendous natural ability to fly on a broomstick and is made Seeker of the Gryffindor Quidditch team.  Flying lessons are never mentioned again in the first book, and as far as I recall, not a single other time in the entire seven books. Harry clearly didn't require them but there were a lot of other students who would have benefited from them, including Hermione.  What amount of tutoring is actually available for those wishing to learn to fly at Hogwarts? Are flying lessons mandatory for first years? Do they continue in subsequent years as well?


I am trying to install cuda-toolkit to my fresh ubuntu-15.10 . After reading the official instructions here http://developer.download.nvidia.com/compute/cuda/7.5/Prod/docs/sidebar/CUDA_Installation_Guide_Linux.pdf   lspci | grep -i nvidia 02:00.0 VGA compatible controller: NVIDIA Corporation G94 [GeForce 9600 GT] (rev a1)  uname -m && cat /etc/*release x86_64 DISTRIB_ID=Ubuntu DISTRIB_RELEASE=15.10 DISTRIB_CODENAME=wily DISTRIB_DESCRIPTION="Ubuntu 15.10"       gcc --version gcc (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010   I downloaded the cuda-repo-ubuntu1504-7-5-local_7.5-18_amd64.deb file and run the following commands:  Installation Instructions:  sudo dpkg -i cuda-repo-ubuntu1504-7-5-local_7.5-18_amd64.deb  sudo apt-get update  sudo apt-get install cuda  But when I try installing cuda I get that message   E: Failed to fetch file:/var/cuda-repo-7-5-local/./cuda-visual-tools-7-5_7.5-18_amd64.deb  Hash Sum mismatch  E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?   I tried apt-get update and everything updated correctly. With --fix-missing? I get   Unable to correct missing packages. E: Failed to fetch file:/var/cuda-repo-7-5-local/./cuda-visual-tools-7-5_7.5-18_amd64.deb  Hash Sum mismatch  E: Aborting install.   Nvidia drivers under additional drivers section  Using NVIDIA binary driver-version 340.96 from nvidia-340(proprietary,tested)   If anyone has anything to suggest or if I did something wrong please help me I am new to Ubuntu as well to cuda . Thank you very much.

When I check for updates, I get a "Failed To Download Repository Information" error.   This is what comes up under details:   W: Failed to fetch gzip:/var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_natty_main_source_Sources  Hash Sum mismatch,  E: Some index files failed to download. They have been ignored, or old ones used instead.


While watching Star Trek Into Darkness, the following two scenes looked funny to me.   In the opening scene, Spock almost dies while trying to save a native population from death by volcano. His death is only averted by exposing the population to the sight of the Enterprise, which might or might not be a worse problem, depending on your perspective. Some time later, McCoy and Dr. Marcus go open a torpedo they know little about, with a very real risk of instant death apparently hanging over their heads.   What I find funny is that these are the kind of tasks that could be easily delegated to a remotely-controlled robot. Bomb-disposal units in the present day never send a person to examine a suspicious device if they can use a robot instead. Why do the enterprise crew not make use of this option? Given how stupendously advanced their technology is, you would think they could have a few mechanical gizmos with a radio link to the bridge, so that they could perform this kind of tasks without putting lives at risk.

Okay, obviously beyond Data and the Soong-type androids. But seriously, we have more robots in our daily life now than there apparently are on Trek. Is there a canon answer why not? It seems like Star Wars is more on the nose in this regard - it’s unclear why all dirty/dangerous/boring work wouldn’t be done by robots (anthropomorphic or not).


If $\{x\}$ denotes the fractional part of $x$ and for $n\in \mathbb{N}$ we define the set $A_{n}=\left\{k \in \mathbb{N}: \{\frac{n}{k}\}  \geq \frac{1}{2} \right\}$. Then how can I try to calculate the sum: $ S_{n}=\sum_{k \in A_{n}} \varphi(k)$ where $\varphi$ is the Euler's totient function. I've tried calculating the sum by hand for integers $1\leq n\leq 10$ and noticed that $S_{n} = n^{2}$ for these, but other than this, I have not found any other patterns.

Let $S(n)$ be $S(n)=\left\{k\;\left|\;\left\{\frac{n}{k}\right\}\right.\geq \frac{1}{2}\right\}$,where $\{x\}$ is the fractional part of $x$  Prove that :  \begin{align} \sum_{k\in S(n)} \varphi(k)=n^2 \end{align}  maybe the fact \begin{align} \sum_{k \leq 2n}\left\lfloor{\frac{n}{k}+\frac{1}{2}}\right\rfloor \varphi(k)=\frac{3n^2+n}{2}\end{align}  and \begin{align} \sum_{k \leq 2n}\left\lfloor{\frac{n}{k}}\right\rfloor \varphi(k)=\frac{n^2+n}{2}\end{align}  can help, but I can't prove these two equations    Edited:Sorry that my question is to prove the two equation before, because I've already known how to relate the problem with these two equations, and I've also known how to prove the second equation from  but I can't solve the first one with the similar method.


Take an object a vertical distance $r$ above the surface of the earth of radius $R$.  The acceleration due to gravity at any $r$ is therefore: $a=\frac{GM}{(R+r)^2}$   Lets say the object falls from rest for $t$ seconds, how far does it fall in this time?  I assume calculus is necessary but get lost in the calculations.  $$a=\frac{dv}{dt}$$ so... $$dv=\frac{GM}{(R+r)^2}dt$$  Where do I go from here or am I even on the right track?  I guess I want an integral where: $$ds=\int_0^t something . dt$$  but I don't know how to get there.

Suppose an object of mass $m$ starts at rest at a radial distance $ r_0$ from a perfectly spherical mass $M$ (where $m << M$), $r_0 > R =$ radius of $M$.    Can we analytically determine when $m$ will hit the surface of the $M$?  In other words, can we analytically solve this initial value problem:  $$ \frac{d^2r}{dt^2} ~=~ - \frac{GM}{r^2} ,$$ $$ \dot{r}(0) ~=~ 0 ,$$ $$ r(0) ~=~ r_0? $$


Regard this . I used normalization instead of normalisation.  Google says "Normalisation is the process of taking data from a problem and reducing it to a set of relations while ensuring data integrity and eliminating data redundancy. Data integrity - all of the data in the database are consistent, and satisfy all integrity constraints."   And "Database normalization, or simply normalization, is the process of organizing the columns (attributes) and tables (relations) of a relational database to minimize data redundancy."     Can you explain it in formal way, please?

I normally write using the American English forms, but for some particular words, I tend to naturally write it in the British manner (like with the word favourite rather than favorite).  Is it wrong to mix both styles? If not *wrong*, does it looks weird?


Is there any way i can open .heic file on ubuntu? It's macos bigsurs dynamic wallpaper. Contains 8-9 wallpaper. I'm on Ubuntu20.05.

A certain cellphone maker has changed the default format of taking pictures to HEIF (.HEIC, High Efficiency Image File Format), without asking the users (although there is still the option to use jpeg/jpg).   Is there an app/program on Ubuntu that can open and/or convert HEIF-pictures and even let them be edited?


Could you tell me, what is the correct form?      "The most preferable length of the internship is/ are 3 months but 2 is/are   also acceptable"   My intuition tells me that should be 'is' but 'are' seems to be more proper for number 3.

When writing about specific quantities, should the verb reflect a singular or a plural value?  Do abbreviations vs. spelled-out words make any difference?  I took 2 ml of water, which was/were then added... Six microliters of protein solution was/were placed in a centrifuge...


I have an  config in /etc/skel/.config/htop/htoprc copied to all new user  home directories. When I run  as a regular user I see the expected settings. However under 18.04 if I ran sudo -s then  Ubuntu would still use my regular user's htoprc from .config and work fine.   On 20.04 I notice when I sudo -s then htop it is no longer reads the user's config from their shell, it creates a new file in /root/.config/htop/htoprc with default htop settings. Is this something new about ? I thought the -s would keep utilizing the calling users shell as opposed to -i which switches to the root user's shell?

In Ubuntu releases prior to Ubuntu 19.10 Eoan Ermine, when I run a command with sudo, that command receives my home directory in the $HOME environment variable. This is the behavior I have long expected and . If I want sudo to reset the $HOME environment variable, so that it refers to the target user's home directory instead of my own, I have to pass the -H option (or -i, though that does more).    ek@Kip:~$ lsb_release -d Description:    Ubuntu 18.04.3 LTS ek@Kip:~$ sudo printenv HOME  # Shows ek's home, not root's. /home/ek ek@Kip:~$ sudo -u as printenv HOME  # Shows ek's home, not as's. /home/ek ek@Kip:~$ sudo -H printenv HOME  # Shows root's home. /root ek@Kip:~$ sudo -Hu as printenv HOME  # Shows as's home. /home/as   When I first upgraded to Ubuntu 19.10, I was surprised to discover that sudo seems to reset $HOME no matter what! I continue to observe this now that 19.10 is released and I've installed updates--both on newly installed systems and one I upgraded to 19.10.  ek@Cord:~$ lsb_release -d Description:    Ubuntu 19.10 ek@Cord:~$ sudo printenv HOME  # Shows root's home, even without -H or -i. /root ek@Cord:~$ sudo -u as printenv HOME  # Shows as's home, even without -H or -i. /home/as ek@Cord:~$ sudo -H printenv HOME  # Also shows root's home. /root ek@Cord:~$ sudo -Hu as printenv HOME  # Also shows as's home. /home/as   I thought this might be due to .  But I checked, and always_set_home does not appear in any Defaults line in my 19.10 /etc/sudoers file.  What makes sudo treat $HOME differently starting in 19.10, and why was this change made? Does this make it safe to use plain sudo in cases where I would previously have used sudo -H?


This must be easy and I have done it a few years ago (I can't recall if it was using a custom python script inside the model) but is there a way to select certain feature classes from a geodatabase to then feed it to another tool (merge in this case)? I tried Model Only tools - Select Data and Iterators - Feature Classes and Datasets to collect values but it doesn't work...  So I need to select all the files that have r_End_ for one merge and r_Start_ for a seperate merge. I had a look at  and  as well as the arcmap help.

I have a folder of shapefiles and each one starts with a code.  There are multiple shapefiles that start with each code, and I would like to create a model in ModelBuilder that will select the shapefiles that have the same code, and append them into the appropriate existing geodatabase feature class.    Is there a way to use a wildcard in the Append tool, like to specify that any and all files in a certain folder starting with 'XPGC*' get appended into the 'Pipe_Grade_Change' feature class?  Or is there a way to use an iterator to accomplish this?


Randomly I texted my teacher regarding tuition fee which I transferred through the bank.  The text was: Money transferred, but I feel some wrong in this text and observed keenly and I found that the correct sentence is Money was transferred. I am embarking curiosity in my mind what is the difference between the two sentences, some knowledge to identify those errors any online tool to detect those errors, remake it to correct one.  PS: Edits are welcome. Sorry for the poor English.

For instance, a train sign might say South bound trains this platform rather than Use this platform to take a Southbound train.  There is an interesting lack of articles and sometimes verbs, is there a name for this style (or a reason for it)?


Rocmen here, a newbie. I was wanting to import 3d character model like a man  and modify it and then animate it. Is that possible in Blender?  Thanks for any help  Rocmen

Since asking for tutorials, videos, resources, links to other content or downloads is considered off topic here, this is a specifically created Community Wiki which gathers resources for Blender and it has been approved by the .  Just write in the appropriate answer/section. If you have concerns, questions, post a  question, so we don't clutter the comments, but you can link your meta question from the comments.  Questions regarding such resources are not allowed anymore, except for very specific and on topic requests (ask on  if you're unsure about your question). Follow the instructions made in the question about how to post, what can be posted, etc.  Learning             Assets    (also see: )   Reference Images/Blueprints (also see: )    Tools    (also see: )      Other   Special Interest ()     Also see the .


Suppose $F$ is a field, let $f(x), g(x), h(x) \in F[x]$ and $d(x)=\gcd(f(x),g(x))$. If $f(x) \mid h(x)$ and $g(x) \mid h(x)$, prove that $f(x)g(x) \mid d(x)h(x)$.

If $\gcd(a,b) = 1$ and $a,b\mid x$ then $ab\mid x$.  My attempt at answering the question:  \begin{align*} x &\equiv 0 \pmod{a}\\\ &\Longrightarrow x\text{ is divisible by $a$}\\\ &\Longrightarrow x = ma\text{ for some integer $m$}\\\ \ \\\ x &\equiv 0 \pmod{b}\\\ &\Longrightarrow  x\text{ is divisible by $b$}\\\ &\Longrightarrow x = mb\text{ for some integer $m$}\\\ \ \\\ x^2 &= (ma)(mb)\\\ x^2 &= (m^2)(ab)\\\ x &= \sqrt{m^2ab}\\\ x &= m\sqrt{a}\sqrt{b} \end{align*} Let $m$ be $k\sqrt{a}\sqrt{b}$. Then \begin{align*} x &= kab\\\ &\Longrightarrow x \equiv 0 \pmod{ab} \end{align*}  Is this correct, if not can someone point me in the right direction?


I'm curious how a photon from an entangled pair, travelling through say a delayed choice quantum eraser experiment, can bounce around between mirrors but remain entangled with its partner photon, when any kind of "observation" of that photon destroys its entanglement.  Surely there is some form of interaction happening at the site of reflection that causes the photon to change its direction. What is special about this type of interaction that does not cause decoherence in the photon's wave function?

In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end we get interference between the various paths. This is fairly easy to observe in the laboratory.  The interference means there is no which-path information stored anywhere in the mirrors. The mirrors are made of 10^20-something atoms, they aren't necessarily ultra-pure crystals, and they're at room temperature. Nonetheless, they act on the photons as very simple unitary operators. Why is it that the mirrors retain no or very little trace of the photon's path, so that very little decoherence occurs?  In general, how do I look at a physical situation and predict when there will be enough noisy interaction with the environment for a quantum state to decohere?


Please help. I'm a student with zero Linux experience and I really want to learn more about it. I am using HP-Pavilion-15-cs3006tx with 1TB storage and 20GB RAM. I installed Ubuntu 20.0.4 via USB drive. After installation, I removed the USB drive and clicked Enter. After turning my laptop on again, I am directly booted to Windows 10. I have been trying to solve this for the past 9 hours non-stop and re-installed Ubuntu four times already. Please help me. Thank you.

I installed Ubuntu on a Dell XPS 13 laptop that had Windows 10 preinstalled on it. I installed it from a USB flash drive on a partition. When I boot my computer I can only boot into Windows 10 and Ubuntu is nowhere to be seen.  If I boot into my USB then I can see that Ubuntu is installed, but I can't get to it from the BIOS boot menu.


The random variables $X$ and $Y$ have the joint density $$f_{X,Y}(x,y)= \left\{\begin{matrix}e^{-y}, \mbox{ } 0\leq x \leq y \le \infty \\ 0,  \mbox{   otherwise}\end{matrix}\right.$$ Evaluate the conditional expectation $E[X|y]$.    I'm not sure if I'm doing this correctly. Please let me know if something is off in my solution. Thanks for reading.  My solution:  I'm not sure if my approach is correct since $f_{Y}(y)$ turns out to be an infinite number. Also in line 4, is the domain correct?  $$E[X|y] = \int_{-\infty}^{\infty}xf_{X|Y}(x|y)dx.$$  $$f_{X|Y}(x|y) = \frac{f_{X,Y}(x,y)}{f_{Y}(y)}.$$    $$f_{Y}(y) = \int_{-\infty}^{\infty}f_{X,Y}(x,y)dx$$   $$= \int_{0}^{\infty}e^{-y}dx = e^{-y}\int_{0}^{\infty}1dx $$  $$=e^{-y}\left [ x \right]\Big|_0^\infty $$  $$ = ??? $$  Thanks in advance for reading this and responding!

The random variables $X$ and $Y$ have the joint density $$f_{X,Y}(x,y)= \left\{\begin{matrix}e^{-y}, \mbox{ } 0\leq x \leq y \le \infty \\ 0,  \mbox{   otherwise}\end{matrix}\right.$$ Evaluate the conditional expectation $E[Y|x]$.    I'm not sure if I'm doing this correctly. Please let me know if something is off in my solution. Thanks for reading.  My solution: (My expected value is negative, which I'm pretty sure can never be the case. Also in line 4 and 8, are the domains correct?)  $$E[Y|x] = \int_{-\infty}^{\infty}yf_{Y|X}(y|x)dy.$$  $$f_{Y|X}(y|x) = \frac{f_{X,Y}(x,y)}{f_{X}(x)}.$$    $$f_{X}(x) = \int_{-\infty}^{\infty}f_{X,Y}(x,y)dy$$   $$= \int_{0}^{\infty}e^{-y}dy $$  $$=\left [ -e^{-y} \right]\Big|_0^\infty $$  $$ = -e^{-\infty}-(-e^{0})=1. $$ $$f_{X}(x) = 1, x \geq 0.$$ Thus,   $$E[Y|x] = \int_{0}^{\infty}-ye^{-y}dy$$  $$= -\int_{0}^{\infty}ye^{-y}dy$$ After integration by parts,  $$E[Y|x] = \left [ ye^{-y}+e^{-y} \right]\Big|_0^\infty$$ $$=0-[e^{0} + 0]=-1$$ Therefore, $E[Y|x] = -1.$  Thanks in advance for reading this long problem and responding!


Let $E$ be a bounded measurable set of $\mathbb{R}^n$.  If every countinuous function $f:E\to\mathbb{R}$ is also uniformly continuous, then $E$ is compact.   Since I do not know topological property of  $f(E)$, it seems that I must use some measure property to show $E$ is closed. However, measure and topology seems not quite relevant.   Thank you!

We have by  Heine–Cantor theorem that:     If $M$ and $N$ are metric spaces and $M$ is compact then every continuous function $f : M \to N$, is uniformly continuous.   Is the inverse of this theorem is satisfied?


I am using WorldView-3 satellite images that have been orthorectified and corrected to sensor reflectance values to compute a set of normalized difference indexes, including NDVI in ArcGIS version 10.31. While I am aware that it is possible to automatically compute NDVI in Image Analysis, I want to try the operation in Raster Calculator since NDVI is not the only index that I wish to compute.   However, whenever I run the operation (with any of the indexes that I am interested in using), the result is always the same. I obtain a binary raster output, in which pixels are either 0 or -1. The exact same pixels, no matter the type of index and bands that I choose. This is weird since when I manually calculate these indexes for the reflectance values in a set of control points, the result shows that the image should lead to an output that as expected ranges from 1 to -1.  The formula that I have been inputting into the raster calculator is the following.  ((NIR2 - Red)/(NIR2 + Red))   To add more context, the site that I am working at is a peninsula in the north of Madagascar. The 0 values are always restricted to the land and the -1 values are restricted to the surrounding ocean and a small lagoon. The WorldView dataset is stored as a 16-bit TIFF file, containing the 8 multispectral bands that the satellite's sensor pics up. To run the raster calculation, I extracted the bands using ArcCatalog and opened them independently in ArcGIS.  Has anyone ever run into a problem like this?   Or does anyone have an idea of what is causing the problem?

I'm trying to calculate the NDVI using raster calculator, but the result is integer instead of decimal.  NDVI = (NIR - RED)/(NIR + RED)   The result is normally in the range -1 to 1, but when i tried to calculate de result is -1, 0 and 1, and it does not have have any number in between like, -0.9 or 0.1. And i need those values so i can classify the result in term of soil occupation


I create colored pencil art and I'm very confused about the whole thing of resolution: A professional print provider is doing the photo shoot of my artwork, and I was just handed an image that is 72 dpi, but the picture is very large. I thought it should be 300 dpi so I could save it into the various sizes I need for mags or printing or submission for shows.  What is the correct way to do this? When I shoot my art myself just for my own use I resize the images to 72 dpi and they then look quite small, the right size for posting on my blog but the 72 dpi image he sent me as mentioned was very large at 72 dpi.  Some advice here please and thank you.  I am new at this and the question was answered but I did not understand a word of it.  Could someone please explain this process in layman's terms please?

(This question is meant to be a resource to direct others to given that this is a common question.)  Given the task of creating an image that will be printed at a certain size, what pixel dimensions and resolution should I be setting my file at?


If $\sum_{n=1}^{\infty}u_{n}$ is convergent and $u_{n}\ge 0 $ Then prove that $\sum (u_{n})^{2}$ is convergent

Suppose $a_n \ge 0$ for all natural numbers $\Bbb{N}$ and $\sum{a_n}$ converges. Is it necessarily true that $\sum{(a_n)^2}$ converges?  I think yes.  Clearly as $a_n \ge 0$ it follows $(a_1+a_2+\dots+a_n)^2 \ge a_1^2+a_2^2+\dots+a_n^2 \ge 0$ and so $(\sum_{n=1}^{\infty}{a_n})^2 \ge \sum_{n=1}^{\infty}{a_n^2} \ge 0$.  As we are told $\sum{a_n}$ converges to say $L$ where $L$ is a real number it follows $L^2 \ge \sum_{n=1}^{\infty}{a_n^2} \ge 0$ and so therefore $\sum{(a_n)^2}$ converges.  Is this correct?


I am inserting face on a rectangle. I want to create a picture frame and I want equal thikness for all "the outer faces" (not like my print screen)[![enter image description here]

I seem to have screwed up something that allows you to inset evenly, I think I have tried every combination of settings in inset and pivot center and even is far from even.  I tried uninstalling and re installing blender 2.71 and get the same result.  The image attached is a simple default cube that I tried to inset evenly.  I have also attached the blend file link  help??


I asked a  5 days ago. Now I know that there are no solutions for what I was searching for.   So there can't be a correct answer, so I never can mark any answer as the correct one. What should I do now? Let the question be unanswered or should I write something?   I won't delete the question, because it's a positive upvoted question, so other users are might also interest in a solution or want know that there is no solution.

I asked a question almost as soon as I got my account. I got a few decent answers, but none of them helped solve my problem. The question has long since become buried by newer questions, and there's still no accepted answer. Unfortunately, because there are quite a few answers with votes, to a casual observer it probably looks like the question was answered and I just neglected to mark an answer as accepted, and the system does not consider it "unanswered".  Or, I asked a question that was a bit more difficult to answer. After waiting for some time, I received no answers, little or no comments, and only a few views. The question does show up in the "unanswered" list, but no one has answered my question.  In either case, what's the protocol for me to try to get this question answered?  I see several options:   Post the question a second time, possibly linking to the original, to get attention for the original question. This is encouraged on sites like Reddit.  However, it's probably not appropriate here, since we're encouraged to check for duplicates and not submit a question that's already been asked by someone else, so this probably falls under that heading. Wait for some kind of wiki-like talk page to be implemented, then post a plea on the talk page for input and hope that activity on the talk page bumps up the question. Edit the question, but do nothing further on the Stack Exchange site. If I edit my post to say that I haven't accepted any of the current answers but am looking for more, then the question might get answered eventually by people browsing through old questions to find something they can answer. Post the question on other sites, but link to my original question on Stack Exchange. People will either answer here, or they'll answer on the other site and I can post the accepted answer here myself.  This might be considered spamming, so it might be better to do this without the link.      For more information, see the "" page in the .


Here's a jsfiddle example of doing it with css, They'll match at any length. But I need it to at minimum be the full height of the viewport/body. In this example, it cuts short when there's only a little content:    I'm not sure what else is possible in css. I'm thinking some sort of javascript div height matching is needed. Really, any solution would work for me, even if it's complicated.  Thanks,  Here's the code from the fiddle:

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I have a layout that is working, but it has one very annoying problem.. when the content is taller than the screen, the background stops.  This is the desired layout in bad-ASCII-art format:  _____________________  _ |    | long    |logo|   | |    | content |    |   | |    |         |    |   | |    |         |    |   | |grad|         |grad|   | Viewport |    |         |    |   | |    |         |    |   | |    |         |    |  _| |    |         |    | |    |         |    | _____________________  |2em| <-20em->| 2em|   ..or with short content..  _____________________  _ |    | short   |logo|   | |    | content |    |   | |    |         |    |   | |    |         |    |   | |grad|         |grad|   | Viewport |    |         |    |   | |    |         |    |   | |    |         |    |   | |    |         |    |   | _____________________  _|   Basically it looks like a single column, with a glow as a column either side. Over the left-glow is a logo. When the content is short, it is still the full-height.  I have tried using the , which fixes the middle column, but then the gradients only extend as far as the content (in the left column, a single &nbsp;, in the right column the logo)    Here is what the layout looks like:    And the problem (when the browser window is shrunk vertically):    Finally, the problem HTML/CSS,


In the terminal, one way to reference home is by using ~/. I don't understand how this works, because the output of file ~/ is:  /home/admin/: directory   and just running ~/ results in:  -bash: /home/admin/: Is a directory   so what's converting ~/ into /home/admin?  ~/ also appears to work in /bin/dash, so I also know it's not bash specific.

I was confused, trying to copy some files from one PC to another. I have it figured out, but the syntax is still confusing to me. This works:  scp ~/Desktop/Volenteer.png jay@server.ip:~j0h/b   which puts Volenteer.png in the folder /home/j0h/b.  However, this doesn't work:  scp ~Desktop/Volenteer.png     jay@server.ip:~j0h/b   This also fails, giving an exit status 1 file not found:  scp ~/Desktop/Volenteer.png     jay@server.ip:~/j0h/b   As does this:  scp ~Desktop/Volenteer.png     jay@server.ip:~j0h/b   So clearly, there is some difference between ~ and ~/ That difference is the presence of /   $~/ bash: /home/j0h/: Is a directory $ ~ bash: /home/j0h: Is a directory   So why in scp, does the ~ resolve to ~/ ? That is a guess, I cant verify that's what is happening.  But it seems inconsistent, and therefore confusing.  Is this a bug in scp? or is there something about tilde I am missing?


I have backed up and restored many a SQL Server database using T-SQL script, but always FROM DISK or TO DISK. I am not a provisioning-concerned database administrator, though, so don't have as much experience with the full range of available backup types.  Now I'm working with a database new to me where the physical_device_name from table msdb.dbo.backupmediafamily for the full backups is a GUID followed by a number, e.g. {F1554525-23BC-48A2-89E0-4069C2D3ACF3}1. How do I use this? Is it tape? Or a physical device name? I have searched online for references to using a GUID in restores or to restoring FROM TAPE and can't seem to find any examples.  Unfortunately at this moment I don't have on-demand access to the server where the backup is and the server doesn't have enough disk space for an extra copy of the database, anyway. But, when I DO get in this situation again, I'd like to know the correct syntax.  RESTORE DATABASE DBName FROM {F1554525-23BC-48A2-89E0-4069C2D3ACF3}1; doesn't look like good syntax to me.  RESTORE DATABASE DBName FROM TAPE = '{F1554525-23BC-48A2-89E0-4069C2D3ACF3}1'; looks more likely. Is it a tape device?  Or is there some additional set of values I need from the backupmediafamily table that will help me know how to write the restore statement (and a RESTORE FILELISTONLY statement, too)?  Note: the log backups look like normal filesystem files. So no issue there.  Additional Note: the problem with the suggested duplicate is that the answers there are less than confident. It could be DPM/VSS or tape. So... some definitive answer, here or there, would be appreciated.

Checking my Native backup this morning something wierd happened. I will describe the problem here.  1) The msdb table backup set shows me the backup was done successfully.  2) The errorlog shows me that the backup was done successfully.  3) The job history doesn't show any entry, even it is successfully or error.  4) Checking the backup media family table the physical device name column shows me something like this: {F2F1E11C-589A-4AAE-8880-0120D8D1998D}1 and other days it shows me the right directory of my backups.  4) The DPM also do system state and database backup after the SQL Server Backup and runs well.  Well.. if anyone need more informations, please let me know.  Thanks. Marcos Freccia @SqlFreccia


If something is moving past me at a relativistic speed, does its gravitational force on me increase as its speed increases? That is, not as if its speed is changing, but if multiple of the same (rest) mass go past me in the same path, is the gravitational attraction at the closest point the same for each, or is it higher the faster it's moving?  As some background, I was recently surprised to see that I should discard the idea of "relativistic mass", so I've been trying to work on that. Please forgive me mixing Newtonian physics with relativity, but I'm trying to get a high level understanding before going into the math too much. I understand now that instead of $F=m_{relativistic}a$ I should use $F=\frac{d}{dt}(\gamma m_0v)$, but what about $F=\frac{Gm_1m_2}{r^2}$? Is that still roughly as it is, or do I need to throw a factor of $\gamma$ in there, or something else entirely?  Yes, I know this is talking about acceleration and so it doesn't really fit into special relativity, and lots of other disclaimers, but I'm hoping for a simple answer to get a general understanding.

If an object was sliding on an infinitely long friction-less floor on Earth with relativistic speeds (ignoring air resistance), would it exert more vertical weight force on the floor than when it's at rest?


Sometimes I see avatar's users with shadow, and if you hover your mouse on them, they expand with a small bio.  Does that feature have a name? Which are the requirements to get that on your profile?

We are experimenting with enhanced user card mouseover popups and have enabled them network wide. You can tell which users will trigger the popup because they have a 3-D drop shadowy look to their gravatar:    Hover your mouse over the gravatar and wait. Note that the user card mouseover popup will only be displayed if the following conditions are met:   Is the profile complete, and long enough? We enforce a minimum length requirement. The user's reputation must be >= 1k  If you have more links than are able to be displayed after truncation, those extra links will be shown in the bottom of the dialog. We order links at the bottom consistently -- if you include a twitter, google plus, linked in, or facebook those links are prioritized. It will be visible on a question and answer detail page, any page with a list of questions, and the /users list. It will not be shown when a question or answer is wiki'd. It will not be shown when excerpt summary is defined as <!-- summary: &nbsp; --> we support explicitly specifying your user card excerpt summary using the following syntax:  <!-- summary: This is my profile, there are others like it but this one is mine. -->   The above example will result in:    This is now mostly complete.  The goal is allow people to show  off how awesome they are inline, without having to click through to the full user profile page.


has two GND and VCC pins:    However,  and  only have one of each. Why is that?    EDIT: I know most MCU's have a lot of 3V3, 5V and GND pins. This is required for connecting the most varied peripherals simultaneously without exceeding max current output. But I have never seen a peripheral with this configuration. Since I never saw a MCU with only one GND and one VCC pin, and there is a lot of nrf24l01 modules with just one pin of each, I would like to know the purpose, since it's supposed that this module should be connected with only one MCU at a time.

What is the reason that most of ICs (e.g. MCU) has multiple (A/D)GND and (A)VCC pins?   If it is to increase performance of an IC, how does it help to performance? or is it easier for the IC designer to connect some pins externally?    some footprint of ICs have a GND connection under the case, how does it help? Would it improve performance of an IC if I draw a GND under the case even if it is not required?


Show that $r$ is the rank of the $n$x$n$ matrix $A\iff A$ has a nonsingular $r$x$r$ submatrix, but any larger square submatrix of $A$ is singular.   I know that to be nonsingular, det $ \neq 0$   I can see this to be true by writing out examples but I am unsure how to approach writing a proof for it.

Let $A$ be a $m \times n$ matrix with entries from some field $F$. Define the determinant rank of $A$ to be the largest possible size of a nonzero minor, i.e. the size of the largest invertible square submatrix of $A$. It is true that the determinant rank is equal to the rank of a matrix, which we define to be the dimension of the row/column space.  It's not difficult to see that $\text{rank} \geq \text{determinant rank}$. If some submatrix of $A$ is invertible, then its columns/rows are linearly indepedent, which implies that the corresponding rows/columns of $A$ are also linearly indepedent.  Is there a nice proof for the converse?


Can I modify the behavior of any dunder method of any class? For example, can I modify the behavior of the __add__ method of the str class? (Totally illogical, but I just want to know if the language is protected from accidental overrides or not.)

Ruby can add methods to the Number class and other core types to get effects like this:  1.should_equal(1)   But it seems like Python cannot do this. Is this true? And if so, why? Does it have something to do with the fact that type can't be modified?  Update: Rather than talking about different definitions of monkey patching, I would like to just focus on the example above. I have already concluded that it cannot be done as a few of you have answered. But I would like a more detailed explanation of why it cannot be done, and maybe what feature, if available in Python, would allow this.  To answer some of you: The reason I might want to do this is simply aesthetics/readability.    item.price.should_equal(19.99)   This reads more like English and clearly indicates which is the tested value and which is the expected value, as supposed to:  should_equal(item.price, 19.99)   This concept is what  and some other Ruby frameworks are based on.


If you have a conducting hollow sphere with a uniform charge on its surface, then will the electric field at every point inside the shell be 0. The reason the electric field is 0 at the center is clear from the symmetry of the sphere, but for a point at a certain distance from the center, shouldn't a net electric field exist?  I saw a similar question on the site but it was vaguely explained.

Say you have a hollow sphere with a uniformly distributed charge on the surface. Why is the electric field everywhere inside the sphere zero?  For the centre, its easy to add the vectors from the surface charges and show they sum to zero because of symmetry.   But can you show me how the field cancels out to zero for points other than the centre using vector addition?


When I am trying to pass an array and evaluate the size of that array using sizeof, it is giving wrong answer whereas it is producing correct result when done in main function:   #include<stdio.h>  #include<string.h>  #include<stdlib.h>   void fun(char c[])  {     printf("in fun, string = %s ,size of c = %d , sizeof c[0]= %d, strlen = %d\n",c,sizeof(c),sizeof(c[0]),strlen(c));  }   int main()  {      char c[]="(a(bc)d(e)f)";      printf("in main, via sizeof -> %d, via strlen -> %d\n",sizeof(c)/sizeof(c[0]),strlen(c));      fun(c);      return 0;  }   The output is:     in main, via sizeof -> 13, via strlen -> 12      in fun, string = (a(bc)d(e)f) ,size of c = 8 , sizeof c[0]= 1, strlen = 12   Compiler is :   gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-28)

First off, here is some code:  int main()  {     int days[] = {1,2,3,4,5};     int *ptr = days;     printf("%u\n", sizeof(days));     printf("%u\n", sizeof(ptr));      return 0; }   Is there a way to find out the size of the array that ptr is pointing to (instead of just giving its size, which is four bytes on a 32-bit system)?


I've heard both of the sentences:     I learn a lot talking to you.      I learn a lot by talking to you.   Does the first one means I learn a lot while I talk to someone and the second I learn a lot as a result of talking to someone?

Which wording with kill should be used here:     He committed a crime (killing/by killing) a bird.   My guess is the answer would be by killing. But I am really confused with the answer killing.   My questions relating to this sentence are:   Which one is correct and why? (or are they both correct?) If one of them is incorrect, why is it incorrect? (or, if both of them are, why?) If they are both correct, what is the difference in meaning? If they are both correct, what is the difference in their grammar?


How can I upload the image and save the image address in the mysql ? 1.I want to upload the image with AJAX 2.And the image address will be stored in the mysql with pdo This is my code:  $(document).ready(function(){     $("#usredit").click(function(){         var name = $("#name").val();         var email = $("#email").val();         var file = $("#file").val();         var image = $("#image").val();         var id = $("#id").val();         var send = true;         $.post("set-ajax.php",{name:name,email:email,file:file,image:image,id:id,send:send},function(data){                     $("#editres").html(data);         });     }); });   ajax.php  if(isset($_POST['send'])){     if(empty($_POST['name']) || empty($_POST['email'])){         echo '
Fill empty fields
';             }else{                 if(isset($_POST['file'])){                     $file = $_POST['file'];                     $tmp = $_FILES['file']["tmp_name"];                     $name = $_FILES['file']['name'];                     $type = $_FILES['file']['type'];                     if (is_uploaded_file($tmp)){                         $ext = array("image/jpg","image/png","image/jpeg");                         if (in_array($type,$ext)){                             $filename = md5($name.microtime()).substr($name,-5,5);                         if(move_uploaded_file($tmp,"user/img".$filename)){                             echo '
Upload done
';                         }else{                                 echo '
Upload failed
';                             }                         }else{                             echo '
Unrelated file
';                         }                     }                 }                 $name = $_POST['name'];                 $email = $_POST['email'];                 $image = $_POST['image'];                 $id = $_POST['id'];                 $resualt = $User->UpdateUserProfile($name,$email,$image,$id);                 if($resualt ){                     echo '
Edit done
';                 }else{                     echo '
Edit failed
';                 }             }

I would like to upload a file asynchronously with jQuery.     $(document).ready(function () {     $("#uploadbutton").click(function () {         var filename = $("#file").val();          $.ajax({             type: "POST",             url: "addFile.do",             enctype: 'multipart/form-data',             data: {                 file: filename             },             success: function () {                 alert("Data Uploaded: ");             }         });     }); });  File <input type="file" id="file" name="file" size="10"/> <input id="uploadbutton" type="button" value="Upload"/>     Instead of the file being uploaded, I am only getting the filename. What can I do to fix this problem?


I have the following string "Dec".  How can I convert this string to the month number 12?  I tried this:  DateTime.ParseExact("Dec", "MMMM", null).Month   This doesn't work.

I need to be able to compare some month names I have in an array.  It would be nice if there were some direct way like:  Month.toInt("January") > Month.toInt("May")   My Google searching seems to suggest the only way is to write your own method, but this seems like a common enough problem that I would think it would have been already implemented in .Net, anyone done this before?


I am working on the following exercise:     Express $w = \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2}$ in polar coordinates.   However $u$ is nowhere defined. Do you know what could be meant by that?

I have a confusion about the following. If we have a function $f:\mathbb{R}^2 \to \mathbb{R}$ of class $C^2$ and we want to calculate the laplacian of this function polar coordinates.  I don't understand what it means. Does it mean we need to calculate :   $$\frac{\partial}{\partial x} (\frac{\partial f(r \cos \theta, r \sin \theta)}{\partial x}) + \frac{\partial}{\partial y} (\frac{\partial f(r \cos \theta, r \sin \theta)}{\partial y})$$  Or does it mean we need to calculate :   $$\frac{\partial ^2 f}{\partial x^2}(r \cos \theta, r \sin \theta) + \frac{\partial ^2 f}{\partial y^2}(r \cos \theta, r \sin \theta)$$  Moreover, I am really confused since I don't understand the fondamental difference between these two expressions.   Thank you !


Imagine you have an array of integer numbers. You need to calculate the probability of encountering some integer sub-array in that list.   For example:   the original list: '1284726437594563495834905834095845634853' which is N integers from 0 to 9.  the question is: what is the probability to encounter '456', order is significant, in that big data set?  my considerations: The are N-2 possible sets of 3 numbers in big list. Each has (1/10)^3 variants. With order significant we need one of them, but any place of the pattern would match. So we have   (1/10)^3 * (N-2)   In case order is not significant, there are n! possible permutations for n items. Thus the formula is   (1/10)^3 * 3! * (N-2)   Am I right?   UPDATE: The digits are distributed randomly, i.e. a possibilities of them are equal. The list is some sequence of these random digits. By "encounter" I mean to have at least one '456' sequence in the given data set.   Looks like my considerations were wrong. Here is a corrected version: A probability to meet at least one sub-array '456':  A probability not to meet any is (1 - (1/10)^3) ^ (N-2), so probability to meet one is   1 - (1 - (1/10)^3) ^ (N-2)   A most probable number of patterns to meet is  (N-2) * 1/10^3

Inspired by Peter Donnelly's talk at , in which he discusses how long it would take for a certain pattern to appear in a series of coin tosses, I created the following script in R. Given two patterns 'hth' and 'htt', it calculates how long it takes (i.e. how many coin tosses) on average before you hit one of these patterns.  coin <- c('h','t')  hit <- function(seq) {     miss <- TRUE     fail <- 3     trp  <- sample(coin,3,replace=T)     while (miss) {         if (all(seq == trp)) {             miss <- FALSE         }         else {             trp <- c(trp[2],trp[3],sample(coin,1,T))             fail <- fail + 1         }     }     return(fail) }  n <- 5000 trials <- data.frame("hth"=rep(NA,n),"htt"=rep(NA,n))  hth <- c('h','t','h') htt <- c('h','t','t')  set.seed(4321) for (i in 1:n) {     trials[i,] <- c(hit(hth),hit(htt))     } summary(trials)   The summary statistics are as follows,        hth             htt          Min.   : 3.00   Min.   : 3.000    1st Qu.: 4.00   1st Qu.: 5.000    Median : 8.00   Median : 7.000    Mean   :10.08   Mean   : 8.014    3rd Qu.:13.00   3rd Qu.:10.000    Max.   :70.00   Max.   :42.000    In the talk it is explained that the average number of coin tosses would be different for the two patterns; as can be seen from my simulation. Despite watching the talk a few times I'm still not quite getting why this would be the case. I understand that 'hth' overlaps itself and intuitively I would think that you would hit 'hth' sooner than 'htt', but this is not the case. I would really appreciate it if someone could explain this to me.


What is the maximum length of a HTTP cookie in different browsers? Does it differ between browsers?  Does the HTTP protocol dictate it?

What is the maximum size of a web browser's cookie's key?  I know the maximum size of a cookie is 4KB, but does the key have a limitation as well?


I am trying to figure out the proper way to handle this. Basically what I want is when a user presses the c key, I want javascript to simulate that after the c key is pressed, a string of other keys are also pressed. So for example the user presses the c key, and then typed would be cool@gmail.com. c being the key they pressed, and ool@gmail.com being keys that were pressed via javascript. What would be the best way to do this?

Is it possible to simulate key press events programmatically in JavaScript?


i am new bie to Linux and wants to configure complete DHCP server and how I can assign ips to clients on Ubuntu or windows machine. will it connect clients automatically to my Linux Ubuntu machine or I may give some configuration.

I am currently at this stage of setting up DHCP, and id just like to know what this output in terminal means? I know I have to edit a file but I do not know which one, and I do not know what to put in it. Ultimately I would like to set up a DHCP server.  matt@matt-R580-R590:~$ sudo tail /var/log/syslog Jan  3 17:35:23 matt-R580-R590 dhcpd: Wrote 0 leases to leases file. Jan  3 17:35:23 matt-R580-R590 dhcpd:  Jan  3 17:35:23 matt-R580-R590 dhcpd: No subnet declaration for eth0 (no IPv4 addresses). Jan  3 17:35:23 matt-R580-R590 dhcpd: ** Ignoring requests on eth0.  If this is not what Jan  3 17:35:23 matt-R580-R590 dhcpd:    you want, please write a subnet declaration Jan  3 17:35:23 matt-R580-R590 dhcpd:    in your dhcpd.conf file for the network segment Jan  3 17:35:23 matt-R580-R590 dhcpd:    to which interface eth0 is attached. ** Jan  3 17:35:23 matt-R580-R590 dhcpd:  Jan  3 17:35:23 matt-R580-R590 dhcpd:  Jan  3 17:35:23 matt-R580-R590 dhcpd: Not configured to listen on any interfaces! matt@matt-R580-R590:~$


Does anyone know the correct word choice between "we" and "us", and explain the reason why? Thanks!

Consider the sentence "I can run faster than 15 miles per hour." Its meaning is clear and to my eyes obviously grammatically correct. Now let me present some variations that have given me trouble for a long time.  I am faster than 15 miles per hour. – To me this is clearly incorrect. Directly comparing me to a speed doesn't seem right. We need to compare my speed to a speed, or me to another person.  I can run faster than him. – Compared to the base sentence, there is a distinct shift in meaning of the comparison. While before I named a speed faster than which I can run, now I am naming a person. It doesn't seem quite right. I realize the parts of speech can change, but my initial objection is that "him" is not a speed.  I can run faster than he. – This seems most correct to me, but still somehow feels objectionable. Is this in fact the correct way to say it? And if so, is it proper as is or need I say "... faster than he can" or even "... faster than he can run?"  I am faster than him. – With "am" instead of "can run" it now seems slightly more correct. But is it?  I am faster than he. – I'm in doubt here. It doesn't seem wrong to me to say, "I am faster than he is" or even "I am faster than he is fast." (Though I suppose that is a given since I could hardly properly compare to some other category as in "I am faster than he is smart.")  My speed is faster than his. – Hmm. This seems more proper as "my speed is greater than his."   So which of these constructions is correct and which is incorrect? Is there a general rule that I can follow? UPDATE The scholarly article  may be of great interest to some readers!  Once we accept that the elided constituent and its antecedent can differ in form, it becomes reasonable to ask how large this difference can be. The answer in Rooth (1992), Fiengo and May (1994), Chung et al. (1995) and subsequent work is that the wiggle room is actually quite small: the elided constituent and its antecedent are allowed to differ only in the realization of inﬂectional morphology. Other than that, both constituents have to be syntactically and lexically isomorphic.


I'd like to reset to a commit and, if there's any new file in my working directory, it should be deleted.  That was the behavior I've expected from git reset --hard [<commit>] but it simply ignores new files while reverting changes on modified files to how it was.  Consider the following example, where I do the following:   delete file main.c commit this change create file main.c revert to previous commit   And expected main.c to no longer exist.  $:~/dev/gittests$ ls main.c $:~/dev/gittests$ rm main.c $:~/dev/gittests$ git add * fatal: pathspec '*' não encontrou nenhum arquivo $:~/dev/gittests$ git status No ramo master Mudanças a serem submetidas:   (use "git reset HEAD <file>..." to unstage)      deleted:    main.c  $:~/dev/gittests$ git commit -m "deleted main" [master 84de2d3] deleted main  1 file changed, 0 insertions(+), 0 deletions(-)  delete mode 100644 main.c $:~/dev/gittests$ ls $:~/dev/gittests$ touch main.c $:~/dev/gittests$ ls main.c $:~/dev/gittests$ git status No ramo master Arquivos não monitorados:   (utilize "git add <arquivo>..." para incluir o que será submetido)      main.c  nada adicionado ao envio mas arquivos não registrados estão presentes (use "git add" to registrar) $:~/dev/gittests$ git log commit 84de2d30505cb6526a2f28918c8b37e4c086db59 (HEAD -> master) Author: ****** Date:   Wed May 15 01:34:27 2019 -0300      deleted main  commit 04382fc20f2fe6dc36ce4443c97f83b786f87781 Author: ***** Date:   Wed May 15 01:14:02 2019 -0300      initial commit $:~/dev/gittests$ git reset --hard 84de2d HEAD is now at 84de2d3 deleted main $:~/dev/gittests$ ls main.c

How do you delete untracked local files from your current working tree?


I am very confused with what actually the chemical potential (chemical potential energy should be the proper name, right?) is. As of right now, I know at least 3 or 4 different definitions of it, which do not seem to have anything in common with each other:  Chemical potential of a species is energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. (wikipedia).  What does energy absorption or release has to do with the change of the Nr. of particles? Is it that when particles are added, this potential increases and when particles leave the system the potential is reduced? And why would the nr. of particles change in the case of phase transition? Phase transition is associated with a density change, but the mass stays intact, meaning the nr. of particles does not change,or no?  In our lecture the professor said that the chemical potential is the energy per particle. Is this correct? And if it is how it's related to the above definition?  For a mixture the chemical potential is it is the partial derivative of the free energy with respect to the amount of the species, all other species' concentrations in the mixture remaining constant. How is this definition the same as what we said above?  For $T=0$ the chemical potential is the fermi emergy. But the fermi energy is just the energy gap between the particle with the lowest energy value and the one with the highest. How is this the same with the energy absorption or release depending from the particle number.   A proper explanation of what this chemical potential (energy?) is and what meaning has, would really help me. Because right now i am doing phase transitions. And for no reason we check the chemical potentials between two phases to say what order type of transition we are currently observing.

Could you please give an intuitive definition of ? It seems that it is an extremely important notion of physics but definitions are really vague.


I'm having trouble with a step in the derivation of the Newton-Euler equations for rigid body translation and rotation when the body frame is not centered at the center of gravity.  The Newton-Euler equations in a frame $G$ attached to the center of gravity are $$ \begin{bmatrix} mI & 0 \\ 0 & J \end{bmatrix} \begin{bmatrix} \dot{v}_G \\ \dot{\omega}_G \end{bmatrix} +  \begin{bmatrix} m\omega_G\times v_G \\ \omega_G\times J\omega_G \end{bmatrix} =  \begin{bmatrix} f \\ \tau_G \end{bmatrix}, $$ where $v_G$ is the body velocity, $\omega_G$ is the body angular velocity about the center of mass, $m$ is the mass of the rigid body and $J$ is the inertia tensor, $f$ is the applied force and $\tau_G$ is an applied torque about the center of mass.  Assume now that we are interested in describing the motion with respect to some other frame $B$ such that the center of mass is at a point $\rho_G$ in this frame (the orientation of the frame $B$ being the same as that of $G$, that is, the frames are related by pure translation). Then $$ \omega_G = \omega_B \\ v_G = v_B - \rho_G\times\omega_B \\ \tau_G = \tau_B - \rho_G\times f $$ from which it follows that the equations become $$ m\dot{v}_B - (m\rho_G)\times\dot{\omega}_B + m(\omega_B\times v_B + \omega_B\times\omega_B\times\rho_G) = f \\ J\dot{\omega}_B + (m\rho_G)\times\dot{v}_B + \omega_B\times J\omega_B + (m\rho_G)\times(\omega_B\times v_B + \omega_B\times\omega_B\times\rho_G - \rho_G\times\dot{\omega}_B) = \tau_B. $$ The derivation I'm following at this point simplifies the second equation to $$ J\dot{\omega}_B + (m\rho_G)\times\dot{v}_B + \omega_B\times J\omega_B + (m\rho_G)\times(\omega_B\times v_B) = \tau_B. $$ I can't understand why this is allowed. Why is it true that $$ \rho_G\times(\omega_B\times\omega_B\times\rho_G - \rho_G\times\dot{\omega}_B) = 0~? $$

I am in search of a simplified version of the derivation of  (both translational and rotational) for a rigid body (3D block) that has a body fixed frame and where the center of mass of the body is not at the center of gravity.  I can find elementary derivations for the same system when the center of mass is at the center of gravity, but not for my system in question.    I am using the derivation as background research for a rotordynamics project that I'm working on.  Any help and or references would be greatly appreciated!  :)


My reputation on Math SE and Meta Math SE differ by almost 12,000 points. I know the meta rep only updates every once in awhile, but I was pretty sure it is every day. It's been almost a year since my reputation was 36K.

While using the top bar to navigate across communities, I noticed that the reputation displayed on meta sites on that list does not match the one of their corresponding main sites:    I have noticed on past situations that reputation gained takes a bit to "update" on the display on Meta sites (that is, if you gain rep on SO, for example, it will take some time for you to see your updated rep on MSO).  However, I have never noticed this behavior here, on the Sites List of the top bar. Furthermore, the "delay" here seems to be more severe, as the "outdated" rep showed is of several days ago (for example, I turned 3k on SO almost exactly a week ago, but the rep shown on MSO is still <3k).  Any idea what could be causing this behavior?    Update: 2 months later this persists: my main site rep updates correctly but their corresponding meta rep remains the same as in the image above.     Update: As per Catija's  I removed the site (MSO) and put it back in, but it didn't update the rep.   However, after removing one site (TWP Meta), waiting at least a day, and then adding it back I see that although the reputations still don't match, the number displayed did changed a bit (previously 29,924 but now 33,112):


I want to wipe a partition quickly.I search the answer in website. such as:   dd if=/dev/zero of=/dev/sda1 bs=16M count=96  shred -v -z -n 1 /dev/sda1  But:  All the commandline,will overwrite with value zero though there is zero.   I think in the partition somewhere have value,but somewhere also have zero.  Want:    Just use commandline but not GUN.Because ddrescue Need to compile and install  dd or shred or other command just overwrite zero to where that there's value is not zero in a partition in Linux.    Update:  My understand is in below   Now:   ddrescue -b 1572864 --generate-mode /dev/zero /dev/sda1 flash.map  // This will create a flash.map   ddrescue -b 1572864 --force --fill-mode=+ /dev/zero /dev/sda1 flash.map //will to fill the patition by flash.map  //1572864byte =16M*96    It's right?What about my understand？

I have a USB flash drive usb 3, the reading speed is much more than the writing speed.  Let's say that 99% of the flash memory is already full with zeros, and I would like to fill it with zeros until 100%, by overwriting all the memory flash with zeros dd if=/dev/zero of=/dev/FLASH.   This process is going to be long, and it will minimize the life expectancy of the flash drive.   I thought, maybe it would be much quicker to check which areas are non-zero, and overwrite only those non-zertos areas with zeros?   Are there anyways of doing this? If it is interesting, I would need all this for security reasons.


I need to have a banner printed for a back lit header on a shelving unit in a retail store with the following dimensions 2’-11" x 1’-0", how many DPI would you recommend printing at?  Thanks in advance for your assistance.

(This question is meant to be a resource to direct others to given that this is a common question.)  Given the task of creating an image that will be printed at a certain size, what pixel dimensions and resolution should I be setting my file at?


Does there exist a smooth bump function $\Phi: \mathbb{R} \rightarrow \mathbb{R} $ such that the sequence $M_k = \max_{x \in \mathbb{R}}|\Phi^{(k)}(x)|$ does not grow faster than exponentially? In general, are there examples of $\Phi$ where the $M_k$ grow (much) slower than in the case of $e^{\frac{1}{x^2-1}}$ (or the like)?    By smooth bump function, I mean a $C^\infty$ function that is $1$ in a neighbourhood of $0$ with compact support.  Pointers to other resources on this are appreciated as well.

I've only seen the bump function $e^\frac1{x^2-1}$ so far.  Where could I find examples of functions $C^∞$ on $\mathbb{R}$ that are zero everywhere except on $(-1,1)$?  Are there others that do not involve the exponential function?  Are there any with a closed form integral?  Is there a preferred function?


I am trying to write simple function that will return sum of two matrices (nested lists). I do not understand why the code below does not work as expected. Note that all printed steps are fine, but the result at the end is not. Code: matrix_a = [[1, 2, 4], [0, 1, 3], [2, 2, 8]] matrix_b = [[0, 3, 1], [5, 4, 2], [8, 2, 6]]  rows = len(matrix_a) columns = len(matrix_a[0]) result = [[0] * columns] * rows for x in range(rows):  for y in range(columns):    result[x][y] = matrix_a[x][y] + matrix_b[x][y]    print(f'[{x}][{y}]: {matrix_a[x][y]} + {matrix_b[x][y]} = {result[x][y]}') print(result)  Output: [0][0]: 1 + 0 = 1 [0][1]: 2 + 3 = 5 [0][2]: 4 + 1 = 5 [1][0]: 0 + 5 = 5 [1][1]: 1 + 4 = 5 [1][2]: 3 + 2 = 5 [2][0]: 2 + 8 = 10 [2][1]: 2 + 2 = 4 [2][2]: 8 + 6 = 14 [[10, 4, 14], [10, 4, 14], [10, 4, 14]]  Could you tell my how to fix it and, what is more important for me, why last row is copied three times?

I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?


I am new to programming and started with R since I need it in my Master's courses can someone help me understand the solution step by step.  awards <- c("Won 1 Oscar.",   "Won 1 Oscar. Another 9 wins & 24 nominations.",   "1 win and 2 nominations.",   "2 wins & 3 nominations.",   "Nominated for 2 Golden Globes. 1 more win & 2 nominations.",   "4 wins & 1 nomination.")  sub(".*\\s([0-9]+)\\snomination.*$", "\\1", awards)   Solution: A vector of character strings containing:  Won 1 Oscar., 24, 2, 3, 2, 1

I don't really understand regular expressions.  Can you explain them to me in an easy-to-follow manner?  If there are any online tools or books, could you also link to them?


I google sold for and see various interpretations.  Chicago Office Tower to Be Sold for Record $850 Million First Wolverine Comic Art Is Sold for Nearly $660,000 Babe Ruth's watch sells for $650,108 Rare Velvet Underground Record Sold for $25k Headed Back to Auction Arrested ship sold for $61m  Sometimes there is an is but sometimes not. What's the difference between sold for and is sold for? Can we use is to be sold for instead of to be sold for?

What is the difference between the examples below?  Generally, in a newspaper, news is based on past tense (things which have already happened).   Then why are headlines written in ways that says: He Kills (shouldn't it be: He Killed)?  For example:  Parliament passes bill vs. Parliament passed bill  Also  He kills his friend vs. He killed his friend  Please help.


I'm struggling with this problem of proof by induction:  For any natural number $n$, prove that $n^3-n$ is a multiple of $3$.   I assumed that $k^3-k=3r$  I want to show that $(k+1)^3-(K+1)=3r$  The final statement is $K^3 +3K^2+2K$  Am I missing something ?

I'm working on a task where I'm a bit unsure if the answer I've got is correct.  Here is the task:     Show by induction that the following assertion is true for all natural   numbers $n$      $n^3 - n$ is divisible by $3$   Here is my answer:     For $n = 1$,   $n^3 - n = 1 - 1$   which is divisible by $3$      Assume the statement is true for some number $n$, that is, $n^3 - n$   is divisible by $3$. Now,      $(n + 1)^3 - (n + 1) = n^3 + 3n^2 + 3n + 1 - n - 1 = (n^3 - n) + 3(n^2 + n) = (n^3 - n) + 3n(n+1)$      which is $n^3 - n$ plus a multiple of $3$.      Since we assumed that $n^3 - n$ was a multiple of $3$, it follows that   $(n + 1)^3 - (n + 1)$ is also a multiple of $3$.      So, since the statement "$n^3 - n$ is divisible by $3$" is true for $n  = 1$, and its truth for $n$ implies its truth for $n + 1$, the statement is true for all whole number $n$.   I would appreciate if someone could go through the task and the answer and see if I've done this correctly.  Thanks a lot!


Lines are missing between healthy and total column  \documentclass{article} \usepackage[table]{xcolor} \usepackage{multirow} \usepackage{makecell} \begin{document} \begin{table} \centering \begin{tabular}{|c|c|cc|c|c|}  \hline & & \multicolumn{2}{c}{BMI} & \\  \multirow{-2.5}{*}{\makecell{Activity level}} &  \multirow{-2.5}{*}{\makecell{Resting heart rate}} &  {Unhealthy} & {Healthy} & \multirow{-2.5}{*}{\makecell{Total}} \\ \hline Inactive & Normal   & 9  & 13 & 22\\           & Abnormal & 16 & \cellcolor{pink}8 & 24\\ Active   & Normal   & 3  & 28 & 31 \\           & Abnormal & \cellcolor{gray}6 & \cellcolor{gray}17 & 23 \\  \hline Total    &          & 34 & 56 & \textbf{100} \\  \hline \end{tabular}   \end{table} \end{document}

Why is there a line missing between Healthy and total column?  \begin{table}[ht]  \begin{center}  \begin{tabular}{|c|cc|c|}  \hline     &\multicolumn{2}{c}{BMI} \\   \multirow{-2.5}{*}{\makecell{Activity level}}& {Unhealthy} & {Healthy} & \multirow{-2.5}{*}{\makecell{Total}} \\  \hline  Inactive  & 25 & 21 & 46\\   Active & 9 &  45 & 54\\   \hline  Total &34 & 56 & \textbf{100}\\  \hline  \end{tabular}   \caption{\label{tab:table-name}Data on activity level, resting heart rate  and BMI}  \label{conting2}  \end{center}  \end{table}


I have a couple of really cool headsets that are both Bluetooth. One is like a beanie that has Bluetooth speakers built in (by Rotibox) and the other one is just a regular headset by Bluedio which is called a Turbine. Both of these headsets have A2DP Sink in them which sounds really good. However, I have Skype calls sometimes and it's nice to be able to talk to people from another room. I also would like to be able to do voice recordings with them which I do often. The problem is that when I set the headset to H2DP Sink it can't access the microphone. If I set the microphone to the high fidelity feedback it switches the speaker to HSP/HFP. Can I fix this and use H2DP Sink and the high fidelity feedback simultaniously? I was able to do this sometimes on Ubuntu Unity 16.10.  I am using Pulseaudio 10.0 on Ubuntu 17.10 with the Deepin Desktop Environment.

I'm trying to use my headphones with my Ubuntu 13.10. My headphones are Nokia BH-905i, which can be connected via Bluetooth or green+pink wires.  If I use bluetooth, voice quality is terrible or microphone doesn't work. If I try to choose "Headset" option from In and Out tabs in Sound Settings, they're disabling each together.  In Out tab, I'm using "High sound quality A2DP", because it betters voice quality.  How could I get my microphone working? Sound out works fine.


I need help placing my items. I'm just starting out so I need explanations. What will seem obvious to you, will not necessarily be so for me :) I have a header that I want to improve. I would like the two images on the right to be superimposed, ie the "reserve" button is above the image. On the other hand, I would like to get to center the middle image. I know the styles are overlapping and the changes I tried through the chrome console are not working. I can't impose the style I want and I can't necessarily find the style that blocks me. If it's possible for you to give me some advice that would be great. Thank you. The link is :  HEADER

Hotel LOGIS LA BORIE en Périgord Noir

Tel. +33 (0 53 28 97 60

  If I addtransform: translateX(calc(100% + 10px)) to the "reservez" button it gives me :  I wanted to use the div containing both images and links as you can see on my code and put display : block but it doesn"t work to have it one above the other... The images are included in a link so if I change only the style of the img the  stays at his place.

I want to overlay one image with another using CSS. An example of this is the first image (the background if you like) will be a thumbnail link of a product, with the link opening a lightbox / popup showing a larger version of the image.   On top of this linked image I would like an image of a magnifying glass, to show people that the image can be clicked to enlarge it (apparently this isn't obvious without the magnifying glass).


I've got a fresh install of the Drupal 8 Beta 12. I'm trying to install the REST UI module:  $ drush dl restui-8.x-1.x-dev  PHP Fatal error:  Class 'Drupal\Core\Session\AccountInterface' not found in /var/www/html/drup/core/includes/bootstrap.inc on line 64 Drush command terminated abnormally due to an unrecoverable error.   [error] Error: Class 'Drupal\Core\Session\AccountInterface' not found in /var/www/html/drup/core/includes/bootstrap.inc, line 64   Does anyone know what's going on here?

I am running Drush version 6.2.0 and the latest Drupal 8 beta on Dreamhosters. When I run drush cc all within the sites directory, I receive the following error immediately after executing the command:     Fatal error: Class 'Drupal\Core\Session\AccountInterface' not found in        /home/mywebsite/mywebsite.com/core/includes/bootstrap.inc on line 63       Drush command terminated abnormally due to an unrecoverable error.                                                                                Error: Class 'Drupal\Core\Session\AccountInterface' not found in       /home/mywebsite/mywebsite.com/core/includes/bootstrap.inc, line 63   Why does it happen? How can I fix this?


I've been using Notepad++ for years now. Since a short while, Notepad++ doesn't start anymore (maybe since a recent Windows Update? Or maybe a plugin update?). The process shows up in the task manager, but it seems to stop executing with a consumed CPU time of less than a second.  However, after re-installing it (V6.9.2) (and also trying the previous version 6.9.1, same effect), I noticed that it does start as usual when executed as Administrator. Note: The behavior is different than the question "" - in that case notepad++ requests Admin rights when started, in my case it doesn't start at all.  I also tried to start it without plugins using the -noPlugins command line option. No effect.  Any idea what could be the cause? What else could I try to reset?

I recently updated my Windows 7 computer with NotePad++ ver. 6.6.9. To do the update I had to run it as Administrator. Now, every time I run Notepad++, it wants to run as Administrator or not at all. I have checked the shortcuts and they are not marked to "Run as Administrator". The problem with this is that NotePad++ can't "see" any of my mapped drives. This is very annoying. How can I get NotePad++ to open normally?


I searched on web about this question and mostly, I found that 14.04 is a way better than 12.04.  but only one answer I found, that say "I am using an old computer and weirdly, I found that 12.04 works better than 14.04"  so I got a doubt, and I want to ask here, this laptop have:  2 GB memory (DDR2) Intel® Core™2 Duo CPU T5450 @ 1.66GHz × 2 Processor Intel® 965GM x86/MMX/SSE2 Graphics 32-bit OS type  which version of Ubuntu, you prefer?

For a given hardware configuration, how do I find out if Ubuntu will run on it? What considerations should I take into account when choosing an Ubuntu version and  such as:    with a lighter desktop than the usual Gnome and Unity  with the even lighter LXDE desktop   Obviously Ubuntu does not run on some processor architectures. So how do I go about choosing the right version and derivate. How can I find out the minmal system requirements?


I am reading Kip Thorne's "Black Holes and Time Warps" and I have a basic question on a topic he is discussing while talking about Einstein and Eddington's disbelief in black holes.  So the general gist is this: a mass falls into a black hole and its mass and energy  are not conserved (ie. lost to the universe).  My question, is: isn't matter and energy actually conserved when an object falls into a black hole?  A objects mass is definitely conserved as it would be added to the singularity's mass.  It might be small comparatively, but where else would it go?  The energy portion of an object (or energy trapped) would be conserved as well.  It might be changed to another form inside the black hole at the point of the singularity but again it's not like it will drip out somewhere)...  (I ask your pardon if I didn't phrase my question correctly as I am not a scientist)...   I do not understand the argument about a BH's not conserving mass / energy.  Can someone explain this to me?

We all know in physics, the law of conservation of energy states that the total energy of an isolated system remains constant—it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another. What happens when said energy ie planets, stars, light etc..enter a black hole?  Does it simply change form or does it disappear from this universe into another? I know many physicists have said all laws start to break down once something enters a black hole but are there any new theories on this? Is it possible it simply turns the energy into a new form like dark matter?


I want to plot a bar graph like below using pgfplot:    This is a hand drawn pic though. I want to show the change of r1 and r2 for a particular variable a. For a=5, r1 is measured at t1 and t2, also r2 is measured at t1 and t2. How can I show this in one plot? I know I can do this in two plots very smoothly. But I dont have enough space in my paper to plot two graphs. Any idea please.

I'm trying to draw a grouped bar plot, but with added dots "on top" to signify outliers in the results.  Currently I have:      \begin{figure}[]       \begin{tikzpicture}         \begin{axis}[             width  = 1*\textwidth,             height = 4.5cm,             major x tick style = transparent,             ybar=1*\pgflinewidth,             bar width=13pt,             symbolic x coords={A,B,C,D},             xtick = data,             enlarge x limits=0.25,             ymax=15,             ymin=0,             legend cell align=left,             legend style={                     at={(1,1.05)},                     anchor=south east,                     column sep=1ex             }         ]             \addplot[style={fill=red,mark=none}]                 coordinates {(A, 4.44) (B,0.1) (C,4.37) (D,4.07)};              \addplot[style={fill=green,mark=none}]                 coordinates {(A, 0.4) (B,0.8) (C,0.3) (D,0.5)};              \addplot[style={fill=blue,mark=none}]                 coordinates {(A, 0.2) (B,0) (C,0.9) (D,0.8)};              \addplot[style={fill=yellow,mark=none}]                 coordinates {(A, 9.59) (B,0.2) (C,8.86) (D,8.62)};          \draw node[fill,circle,scale=0.5]{} (axis cs:A,7);         \draw node[fill,circle,scale=0.5]{} (axis cs:B,11);         \draw node[fill,circle,scale=0.5]{} (axis cs:C,3);         \draw node[fill,circle,scale=0.5]{} (axis cs:D,12);          \legend{C1,C2,C3,C4}       \end{axis}     \end{tikzpicture} \end{figure}   This draws the grouped plots etc, but the "dots" always appear at the (0,0) position, ignoring the relative coordinates. See the picture below, where it is close to the "A". Ideally, I'd like to position such a dot above every bar in the graph. How can I properly specify the coordinates?


This is my third attempt to do a simple share of an external hard drive between two Ubuntu 18 computers. I have worked with half a dozen help documents on the web and none of them worked and they all had different instructions.   I would prefer to use the samba GUI and the option to right click on a folder and share it but even with samba users set I get nothing. Setting the share to allow all users does nothing.   I have uninstalled and reinstalled samba to get a clean version. The only thing that has happened so far is that the shares are visible on the second computer but get an error that it cannot log on to windows share.  Is there a tutorial available?

I have a desktop (Ubuntu 13.04 & Win 7 Home Premium) and a Laptop (Ubuntu 12.04), both having WiFi adapters. I also have a WiFi router connected to internet which both my computers can access.  I want to share files between my desktop and my laptop using WiFi (similar to Homegroup on Windows 7 but without using Ethernet cables).  How do I set-up that?  I want to share files using both OSs, if anyone have have information about sharing files with any of the OS please answer!


Rational numbers are in 1-1 correspondence with natural numbers. For example, let's consider enumeration mentioned in wikipedia:  ()  The above mentioned enumeration makes a sequence: $q_1, q_2, ...$. In other words, $q$ is a function form $\mathbb{N}$ to $\mathbb{Q}$.   Function $q$ is not monotone (i.e. - neither descending nor ascending): it is not necessarily true that for every $i$ $q(i) < q(i+1)$.  At the same time, there exist unique total order on all rational numbers. Because of that I wonder, is there (or why isn't there) a permutation $p: \mathbb{N} \xrightarrow{} \mathbb{N}$ such that $q\circ p$ becomes monotone: $$q_{p_1} < q_{p_2} < ... $$ If such permutation does not exist - why?  Please note, I understand the controversy that if such order would existed, there would have been infinite number of other rationals in between of two subsequent rationals.  Edit: Thanks for the reference to a similar question, I just don't think explanation there is evident enough. It is even more puzzling, because the number of permutation has a next level of cardinality (continuum) and yet - in such a rich set there is no single permutation that will bring order. Or maybe there is?  Edit 2: The initial question was mainly about existence of a permutation. Whether such permutation is incomprehensible to write down or does not exist at all. If it does not exist - why and what can be concluded from that.

This is problem #6 from Section 1.2 of Ash's Real Variables With Basic Metric Space Topology.   I am asked to show that it is impossible to list the rational numbers in increasing order.   While I know it is possible to list a finite subset of the rational numbers in increasing order, I was wondering if the reason for the impossibility in this case is because there is no least element of $\mathbb{Q}$?   I mean, it's possible to impose an ordering on $\mathbb{Q}$ (correct me if I'm wrong, but it seems possible to compare any two rationals).  But the set $\mathbb{Q}$ is of course, a subset of itself, and the Well-Ordering Principle says that a set $S$ is Well-Ordered only if any subset of $S$ contains a minimal element. Since $\mathbb{Q}$ does not contain a minimal element, it does not appear that it is a Well-Ordered set.   Is this the correct idea as to why it's impossible? If not, could somebody explain to me what the correct idea is and a strategy for proving it?  Thank you ahead of time.


Certain categories have the property that for every morphism $f:A\to B$ can be decomposed into an epimorphism and monomorphism. with some intermediate object $C$. e.g. Grp has this property.  Is there a name for this so I can look it up?

The category Set has the property that any morphism f can be decomposed into an epimorphism $e$ and a monomorphism $m$ with $f$ = $m\circ e$. (The intermediary set object is the image of $f$.)  Is there a name for this construction?  Is there a name for this property of categories?  In Set, the intermediary object is unique up to isomorphism. Is this the case for all categories with the property?


When I try to use the command get from sftp, I get the error saying that it is not a normal file.  Is there a way around this?

When I try to use sftp to transfer a directory containing files, I get an error message:  skipping non-regular file directory_name   The directory contains a couple of files and two subdirectories.  What am I doing wrong?


For any two $n \times n$ real symmetric and positive definite matrices $B$ and $C$, is it always possible to find a third real symmetric and positive definite matrix $A$ such that $ABA=C$? If not, give a counter example in a $2 \times 2$ case?

If $A=CBC$, where $A$,$B$,$C$ are symmetric matrices and $A$,$B$ are given find $C$.  $A$,$B$,$C$ are assumed to be real valued and $B$ is positive definite matrix. Does the unique solution always exist ? What additional assumptions are needed to obtain unique solution.


This question is in response to an answer on another question.  Due to my lack of reputation on this SE I couldn't comment on the answer.  Based on JonTheMon's answer to  , destroying a creature that gives Haste to an artifact creature would remove Haste from the newly summoned artifact creature.  But then he goes on to say that the activated Tap ability would be allowed.  How?  According to the official rules on Haste (), tapping or untapping falls under the same rules as attacking.  702.10b.  If a creature has haste, it can attack even if it hasn't been controlled by its controller continuously since his or her most recent turn began.  702.10c.  If a creature has haste, its controller can activate its activated abilities  whose cost includes the tap symbol or the untap symbol even if that creature  hasn't been controlled by that player continuously since his or her most  recent turn began.

I'm a relatively new player to Magic: the Gathering. I was reading  to try to understand exactly when it's okay to cast instants (e.g. ) and use some abilities (e.g.  should be tappable sometime during other peoples' turns), but I don't seem to be making much progress: as I come to understand some things, others make less sense.  My confusion is boundless  For instance: to cast  one needs priority. Spells go on the stack, and priority gets passed at some points (I have no idea when), and effects on the stack are resolved when both players have passed priority. But when is that? I can't find any mention of when the other player gets the priority to cast an instant, except on their own turn. Furthermore,  states that during the Main Phase:     505.4. Second, the active player gets priority. Players may cast spells and activate abilities. The active player may play a land.   So players (plural) may cast spells, but only the active player has priority, so only the active player can cast an instant. The turn rules, and the rules on , never mention any point at which the other player gets priority, so when can they possibly Cancel?  In addition, you can only cast a spell when the stack is empty, so the entire stack must be able to be resolved in your turn at some point.  I need an explanation!  I could go on a bit more. There is also  which can be overloaded to "Counter each spell you don't control", which seems like it could only possibly work with an understanding of the stack.  Could someone explain, in simple English:   When can Instants be cast? When can tap abilities be used? What do Instants and abilities have to do with the Stack and Priority?


I am running out of disk space with /var system file and noticed /var/log/jenkins/jenkins.log file is occupied 7 GB. Can i safely remove this log file ?

I never view or care about files in /var/log/  and want to avoid  wasting my system resources (CPU, RAM, I/O, etc.). Are any regular files in /var/log/ necessary for some core Debian program (e.g. apt, aptitude, etc.) to work?


I have query object  var q = {     age: 10,      'profile.contry': 'india' };   Now I duplicate the q variable and remove key from a duplicate variable.  var duplicateQ = q; delete duplicateQ['profile.contry']; // I have removed 'profile.country' from duplicateQ.  console.log(q); //Object { age: 10 } console.log(duplicateQ); //Object { age: 10 }   Why are both the variables affected? How can I remove the property from only one of them?

What is the most efficient way to clone a JavaScript object? I've seen obj = eval(uneval(o)); being used, but . I've done things like obj = JSON.parse(JSON.stringify(o)); but question the efficiency.  I've also seen recursive copying functions with various flaws.  I'm surprised no canonical solution exists.


I want to scroll down a page that is coming inside a form, not on the main page.   I tried this code:  JavascriptExecutor jse = (JavascriptExecutor)driver; jse.executeScript("window.scrollBy(0,250)", "");     The above code is not able to pick the scroll bar as it is not in the main page

<div id="findingTblBody" class="tablebody" infinite-scroll-distance="2"  infinite-scroll="loadMoreData()" style="width: 819px;">   I want to scroll to the bottom of div mentioned above.     I am trying with this -   do {     driver.findElement(By.xpath("//div[@id='findingTblBody']")).sendKeys(Keys.PAGE_DOWN);     Thread.sleep(6000);     scroll_count++; } while(scroll_count<20);   I am receiving error as - org.openqa.selenium.WebDriverException: unknown error: cannot focus element  How to scroll my web page up to that element & click?


In Minecraft, is there any way to make tools indestructible (without using mods)? I want to make some tools indestructible (for an adventure map). Is it possible to do this using enchantments (or a command of some kind?)


I have encountered different matrix of operator "the Square Root of NOT gate". For example, : $\sqrt {NOT}  = \frac{1}{2}\left( {\begin{array}{*{20}{c}} {1 + i}&{1 - i}\\ {1 - i}&{1 + i} \end{array}} \right)$ And  is given: $\sqrt {NOT}  = \frac{1}{{\sqrt 2 }}\left( {\begin{array}{*{20}{c}} 1&{ - i}\\ { - i}&1 \end{array}} \right)$ Applying them to the vector $\left| 0 \right\rangle  = \left( {\begin{array}{*{20}{c}} 1\\ 0 \end{array}} \right)$, we get different results: $\sqrt {NOT} \left| 0 \right\rangle  = \frac{1}{2}\left( {\begin{array}{*{20}{c}} {1 + i}&{1 - i}\\ {1 - i}&{1 + i} \end{array}} \right)\left( {\begin{array}{*{20}{c}} 1\\ 0 \end{array}} \right) = \frac{1}{2}\left( {\begin{array}{*{20}{c}} {1 + i}\\ {1 - i} \end{array}} \right)$ $\sqrt {NOT} \left| 0 \right\rangle  = \frac{1}{{\sqrt 2 }}\left( {\begin{array}{*{20}{c}} 1&{ - i}\\ { - i}&1 \end{array}} \right)\left( {\begin{array}{*{20}{c}} 1\\ 0 \end{array}} \right) = \frac{1}{{\sqrt 2 }}\left( {\begin{array}{*{20}{c}} 1\\ { - i} \end{array}} \right)$ Where is the correct matrix of the operator $\sqrt {NOT} $ specified?

. For instance I can define either of the two for square root of $X$: $$\sqrt{X}^{(1)} \equiv \frac{1}{\sqrt{2 i}} \begin{pmatrix} 1 & i \\ i & 1 \end{pmatrix}$$ Or : $$\sqrt{X}^{(2)} \equiv \sqrt{NOT} = \frac{1}{2} \begin{pmatrix} 1+i & 1-i \\ 1-i & 1+i \end{pmatrix} \neq \sqrt{X}^{(1)} $$ We notice that those two matrices do not differ by a global phase: they really act differently on quantum state. Now, it is frequent in the litterature to simply see $\sqrt{X}$ or $\sqrt{Y}$ without further explanations. To be generic I consider $M$ a matrix in which I will consider its square root. As long as we do $\sqrt{M} \sqrt{M}$ whatever the definition taken it doesn't matter. However I if we have calculations involving $\sqrt{M}$ without having it directly squared, the result might depend on the choice we took for the square root. My question Is there a uniform convention in quantum information to define square root of matrices ? Or more specifically square roots of Pauli ? Or each reference must specify which convention they take ?


Or did the end of the movie mean that all Kryptonians were completely extinct?   I was a bit confused by the end because it seemed to suggest that all kryptonians were completely extinct. But Jor-El couldn't have known and did not plan on having Zod follow his son to earth, especially with one of those birthing chambers in tow. So he must have assumed that there was another way..  Is it possible that Superman can still use the codex?

SPOILERS:     Jor-El puts Krypton's DNA codex into Kal-el 's DNA. Jor-El seems totally against the idea of artificial birth from the get go of the movie. Kal-El fights with General Zod for the codex. Kal-El destroys the genesis birthing chamber   Hence my question, what was the point of putting the Kryptonian codex into Kal-El DNA if Jor-El never intended for Kal-El to use them? Rather than say.. destroy the DNA codex in the first place? Sure that would make for a quick movie plot, but was there an underlying reason for porting the codex to Kal-El?


Regression to the mean is a statistical phenomenon where in the long run, the results of an experiment average out. Taking the example of one's results on a test, if we've had a string of good outcomes, then the next result is likely to be less satisfactory because things even out, right? If so, how can the probability of success in the next test still be the same as that of the previous tests? How can the gambler's fallacy still be false if we know things must even out?

On the one hand, I have the regression to the mean and on the other hand I have the .  Gambler’s fallacy is defined by Miller and Sanjurjo (2019) as “the mistaken belief that random sequences have a systematic tendency towards reversal, i.e. that streaks of similar outcomes are more likely to end than continue.” For example, a coin that’s fallen heads several times in a row will be thought to be disproportionately likely to fall tails on the next trial.  I have had a good performance in the last game and, according to the regression to the mean, probably I will have a worse performance in the next game.  But according to the gambler's fallacy: Consider the following two probabilities, assuming a fair coin   probability of 20 heads, then 1 tail = $0.5^{20} × 0.5 = 0.5^{21}$ probability of 20 heads, then 1 head = $0.5^{20} × 0.5 = 0.5^{21}$   Then...  Consider a simple example: A class of students takes a 100-item true/false test on a subject. Suppose that all students choose randomly on all questions. Then, each student’s score would be a realization of one of a set of independent and identically distributed random variables, with an expected mean of 50.  Naturally, some students will score substantially above 50 and some substantially below 50 just by chance. If one takes only the top-scoring 10% of the students and gives them a second test on which they again choose randomly on all items, the mean score would again be expected to be close to 50.  Thus the mean of these students would “regress” all the way back to the mean of all students who took the original test. No matter what a student scores on the original test, the best prediction of their score on the second test is 50.     In special If one takes only the top scoring 10% of the students and   gives them a second test on which they again choose randomly on all   items, the mean score would again be expected to be close to 50.   According to the gambler's fallacy shouldn't it be expected the same probability for the scoring and not necessarily more likely close to 50?  Miller, J. B., & Sanjurjo, A. (2019). How Experience Confirms the Gambler's Fallacy When Sample Size Is Neglected.


I have some objects that were made by joining two objects together. This results in a plane that cuts through the object (see below):    I already removed the doubles, but is there some way I can remove the plane itself, so the four vertices there go away?

I dont need this vertices and/or edge. What is the best way to get rid of them?


A newbie here.  Can someone help me understand what are the effects of running the following command from a directory:  sudo chmod -R 777 *  Will it effect the whole file system or the contents of that particular directory?  Thanks

This is a  about File Permission and Why 777 is "destructive".   I'm not asking how to fix this problem, as there are a ton of references of that already on Server Fault (reinstall OS). Why does it do anything destructive at all?  If you've ever ran this command you pretty much immediately destroy your operating system. I'm not clear why removing restrictions has any impact on existing processes. For example, if I don't have read access to something and after a quick mistype in the terminal suddenly I now have access well... why does that cause Linux to break?


public static void main(String[] args) {      CashRegister myCashRegister = new CashRegister();      Item item = myCashRegister.getItem(123456);    public class CashRegister {     public Item getItem(int barcode) {         return this.getItem(barcode);     }    public class Item {      public int getBarcode(){         return barcode;     }   I am creating an item object in main and trying to get the item's barcode through a Cash Register class. I end up getting "Exception in thread "main" java.lang.StackOverflowError".  I do have a getBarcode method in the item class, but kept getting errors because barcode is an int, and so I cannot return an int for the Item getItem method.  Please put me in the right direction towards getting the item's barcode. Thank you.

What is a StackOverflowError, what causes it, and how should I deal with them?