I've recently understood de Broglie's hypothesis, and I understand that a necessity for electrons to show diffraction is that the size of the aperture they pass through must be of the order of their de Broglie wavelength. So exactly what would happen if (if) I were to walk through a door of a size of the order of my de Broglie wavelength? If a number of people of the same order of masses did so?

Many introductory quantum mechanics textbooks include simple exercises on computing the de Broglie wavelength of macroscopic objects, often contrasting the results with that of a proton, etc.  For instance, this example, taken from a textbook:     Calculate the de Broglie wavelength for      (a) a proton of kinetic energy 70 MeV      (b) a 100 g bullet moving at 900 m/s   The pedagogical motivation behind these questions is obvious: when the de Broglie wavelength is small compared to the size of an object, the wave behaviour of the object is undetectable.  But what is the validity of the actual approach of applying the formula naively? Of course, a 100g bullet is not a fundamental object of 100g but a lattice of some $10^{23}$ atoms bound by the electromagnetic force. But is the naive answer close to the actual one (i.e. within an order of magnitude or two)? How does one even calculate the de Broglie wavelength for a many body system accurately?


I am working on an exercise from Zorich's Mathematical Analysis. The problem reads: If $a_{n}\ge a_{n+1}>0$ for all $n\in\mathbb{N}$ and the series $\displaystyle\sum_{n=1}^{\infty}a_{n}$ converges then $a_{n}=o\left(\frac{1}{n}\right)$ as $n\to\infty$; I understand that $a_{n}=o\left(\frac{1}{n}\right)$ means $a_{n}=\alpha(n)\cdot\frac{1}{n}$ where $\alpha(n)\to 0$ as $n\to\infty$. So let $\alpha(n)=n\cdot a_{n}$, then $a_{n}=\frac{\alpha(n)}{n}$, but I cannot seem to fully reason out from convergence of $\displaystyle\sum_{n=1}^{\infty}a_{n}$ to $\displaystyle\lim_{n\to\infty}\alpha(n)=0$. My partial result reasoning is as following: Since $a_{n}\ge a_{n+1}>0$, follow Cauchy's proposition that $\displaystyle\sum_{n=1}^{\infty}a_{n}$ converges if and only if $\displaystyle\sum_{k=1}^{\infty}2^{k}a_{2^{k}}$ converges. Therefore, $$\sum_{k=1}^{\infty}2^{k}a_{2^{k}}=\sum_{k=1}^{\infty}2^{k}\frac{\alpha\left(2^{k}\right)}{2^{k}}=\sum_{k=1}^{\infty}\alpha\left(2^{k}\right)$$ Since it converges, it is necessary that $\displaystyle\lim_{k\to\infty}\alpha\left(2^{k}\right)=0$. But that is only a subsequence of $\alpha(n)$. (added per 's suggestion - thanks) Further from $a_{n+1}\ge a_{n}$ we have \begin{align*}     &a_{n}\ge a_{n+1}>0 \Rightarrow\frac{\alpha(n)}{n}\ge\frac{\alpha(n+1)}{n+1}>0\\     \Rightarrow&\frac{\alpha(n+1)}{\alpha(n)}\le\frac{n+1}{n}=1+\frac{1}{n}\\     \Rightarrow&\frac{\alpha(n+2)}{\alpha(n)}=\frac{\alpha(n+2)}{\alpha(n+1)}\cdot\frac{\alpha(n+1)}{\alpha(n)}\le\left(1+\frac{1}{n+1}\right)\left(1+\frac{1}{n}\right)<\left(1+\frac{1}{n}\right)^{2}\\     &\quad\vdots \end{align*} So if $n=2^{k}$, then $2^{k+1}=2\cdot 2^{k}=2n$, thus \begin{align*}  \Rightarrow&\frac{\alpha(2^{k}+1)}{\alpha(2^{k})}\le 1+\frac{1}{2^{k}}\\  \Rightarrow&\frac{\alpha(2^{k}+2)}{\alpha(2^{k})}=\frac{\alpha(2^{k}+2)}{\alpha(2^{k}+1)}\cdot\frac{\alpha(2^{k}+1)}{\alpha(2^{k})}<\left(1+\frac{1}{2^{k}}\right)^{2}\\  &\quad\vdots\\  \Rightarrow&\frac{\alpha(2^{k+1}-1)}{\alpha(2^{k})}=\frac{\alpha(2^{k+1}-1)}{\alpha(2^{k+1}-2)}\cdot\frac{\alpha(2^{k+1}-2)}{\alpha(2^{k+1}-3)}\cdots\frac{\alpha(2^{k}-1)}{\alpha(2^{k})}<\left(1+\frac{1}{2^{k}}\right)^{2^{k}-1} \end{align*} But we know $$\displaystyle\lim_{k\to\infty}\left(1+\frac{1}{2^{k}}\right)^{2^{k}-1}=e$$ Thus $\alpha(2^{k}+d)<e\cdot\alpha(2^{k})$ is bounded for $d<2^{k}$, so $$\lim_{n\to\infty}\alpha(n)\le\lim_{k\to\infty}e\cdot\alpha(2^{k})=e\cdot\lim_{k\to\infty}\alpha(2^{k})=e\cdot 0=0$$ Hope I got it right..

I'm studying for qualifying exams and ran into this problem.  Show that if $\{a_n\}$ is a nonincreasing sequence of positive real numbers such that $\sum_n a_n$ converges, then $\lim_{n \rightarrow \infty} n a_n = 0$.  Using the definition of the limit, this is equivalent to showing \begin{equation} \forall \varepsilon > 0 \; \exists n_0 \text{ such that } |n a_n| < \varepsilon \; \forall n > n_0 \end{equation} or \begin{equation} \forall \varepsilon > 0 \; \exists n_0 \text{ such that } a_n < \frac{\varepsilon}{n} \; \forall n > n_0 \end{equation} Basically, the terms must be bounded by the harmonic series. Thanks, I'm really stuck on this seemingly simple problem!


I have the following theorem:  If $a = p^{n_1}_1 p^{n_2}_2$ ... $p^{n_k}_k, b = p^{m_1}_1 p^{m_2}_2$ ... $p^{m_k}_k$, then  $gcd(a, b) = p^{min(n_1, m_1)}_1 ... p^{min(n_k, m_k)}_k$  How can I prove it? Any solution or hint?

How should I approach obvious proofs like these    I have been trying but couldn't find an elegant way to work these. Any help is highly appreciated ! Especially looking for a nice proof/hint for first problem


I have the following python code in main which runs my program each 5 seconds def main():     while True:         now = datetime.strptime((datetime.now().strftime("%H:%M")), "%H:%M")         if datetime.strptime('23:59', "%H:%M") > now > datetime.strptime('07:30', "%H:%M"):             start_time = time.time()             while execute_data():                 time.sleep(5.0 - ((time.time() - start_time) % 5.0))  execute_data(): function once in 40 minutes does a job which takes a lot of time (nearly 3 min) when it finished its job my program goes crazy and runs once in every half second for example. How can I solve this?

I want to repeatedly execute a function in Python every 60 seconds forever (just like an  in Objective C). This code will run as a daemon and is effectively like calling the python script every minute using a cron, but without requiring that to be set up by the user.  In , the solution appears to effectively just  for x seconds. I don't need such advanced functionality so perhaps something like this would work  while True:     # Code executed here     time.sleep(60)   Are there any foreseeable problems with this code?


I have the following problem:  Let $X_1,X_2,...X_N$ be a sequence of independent Bernoulli random variables. Let $p\in (0,1)$ and $P(X_i=1)=p, P(X_i=0)=1-p.$ What is the expected value $T_{01}$, the number of $0$'s and $1$'s, before (and including) the sequence "$01$".  This is what I have tried to come up with so far: Basically there are three possible "events" that I have to consider:  The event that the first slot is a $1$, the next $k-1$ slots are $0$'s and the $k$-th slot is a $1$. For example, the event could look like this:  $$\color{green}{1}\color{blue}{0000000}\color{red}{1}000$$  The event that the first $k-1$ slots are $0$'s and the $k$-th slot is a $1$: $$\color{blue}{0000000}\color{red}{1}001$$  The event that the first $k-2$ slots are $1$'s the $k-1$ slot is a $0$ and the $k$-th slot is a $1$ $$\color{green}{111111111} \color{blue}{0}\color{red}{1}011$$   I know from this MIT OCW Lecture () that the proabability mass function (PMF) for such an experiment is given by: $$p_{Y_k}(t)=\begin{pmatrix}t-1 \\ k-1\end{pmatrix}p^k (1-p)^{t-k}$$ This gives the probability of $k$ events in $t$ time. My question: My problem comes from the fact that I don't want to find the arrival time of $k$ events. I am looking the expected value of a very specific event. The event $01$. Do I just find the probabilities of the three cases I listed above and multiply them together? Figuring out the possible cases seems like a very tedious and time consuming way to do it. How can I approach problems like this? Is there some "recipe" that I can follow that extends to similar problems such as finding $T_{101}$ (the expected numbers of $0's$ and $1's $ until the sequence $101$? I want to add another example that I tried to solve based on the answers and the comments: Question: Find the expected number of $0$'s and $1$'s before the sequence $11$. In other words find $E[T_{11}]$: $$\begin{align}E[T_{11}]&=p\left(E[T_{11}] \space \lvert \space X_1=1 \right)+(1-p)\left( E[T_{11} \space \lvert \space X_1=0] \right) \\  \end{align}$$ For the first term: $$\begin{align} E[T_{11} \space \lvert \space X_1=1]&=p\left(E[T_{11} \space \lvert \space X_1=1, X_2=1] \right)+(1-p)\left(E[T_{11} \space \lvert \space X_1=1, X_2=0] \right) \\ &=\underbrace{2p}_{\text{Achieved $11$ in two trials}}+\underbrace{(1-p) (2+E[T_{11}])}_{\text{cycled back to starting state wasting two trials}} \end{align} $$ For the second term: $$E[T_{11} \space \vert \space X_1=0]=\underbrace{1+E[T_{11} ]}_{\text{Cycled back to starting state but having wasted one trial}}$$ Combining the terms and solving for $E[T_{11} ]$: $$\begin{align} &E[T_{11}]=p(2p+(1-p)(2+E[T_{11}]))+(1-p)(E[T_{11}]+1) \\[10pt] &\iff E[T_{11}]= 2p+p(1-p)E[T_{11}])+(1-p)E[T_11]+(1-p) \\[10pt] & \iff E[T_{11}]-p(1-p)E[T_{11}]-(1-p)E[T_{11}]=p+1 \\[10pt] &\iff E[T_{11}](1-p+p^2-1+p)=p+1 \\[10pt] & \iff E[T_{11}]=\boxed{\frac{p+1}{p^2}}\end{align}$$ Assuming the probability $p=\frac{1}{2}$ $$\implies E[T_{11}]=6$$

Suppose you ﬂip a fair coin repeatedly until you see a Heads followed by a Tails. What is the expected number of coin ﬂips you have to ﬂip?  By manipulating an equation based on the result of the first flip, shown at this link:    the answer is 6. This also makes sense intuitively since the expected value of the number flips until HH or TT is 3. But is there a way to tackle this problem by summing a series of probabilities multiplied by the values?  Thank you!


For the AppExchange Security Review, do we need to check FLS on a Dynamic SOQL WHERE clause as well?  Ex: If Contact.My_Custom_Field__c is not visible to the logged in user, then the following SOQL would be a violation of FLS?  SELECT Id FROM Contact WHERE My_Custom_Field__c = 'Oh really'

I know this sounds like a standard question, so please bear with me.  Recently our Security Reviews fail due to CRUD/FLS violations. The highlighted codelines include almost every SOQL Query in the application.  Our approach is usually as follows:   In case of displaying data on VF pages we either use sObjects fields or use the platform methods to check the accessibility of the fields In case of domain logic triggered by the user (e.g. by clicking a button on a VF page) we have a helper class that checks every field to be updated before doing the DML operation.   Up until recently this approach has worked fine (and passed pervious Security Reviews). As mentioned above the latest Security Review results seem to require us to check every field in a SOQL query for accessibility even if it is never displayed back to the user.    Let's suppose the following program flow as an example:   Query an object with some fields Perform some modification on said fields Perform an update on the sObject to save the modification using a helper class which checks for the required CUD/FLS rights for the modified fields   As I see it there is no need for checking field accessibility in step 1 in that case (since nothing is displayed back to the user and the dml operation is already protected). Is that correct or am I missing something? So is it really required to do an accessibility check for every SOQL Query in the code?  Another question would be how to handle background operations in that case like data purging. These have either to be running in system mode (which causes issues during the Security Review) or require the job to be started by a user with the appropriate access rights (which can be error prone and is not that user friendly). Is there any best practice regarding that.  Unfortunately I could not find a question targeting exactly that issue. Most of the questions I have found are related to how to perform that check (like  or ). So please apologize in case the question was already answered (I would really appreciate a link to the answer then).    Thanks for your time and help.  Mathias


Working on the structure of this domain     Wondering if the lenght of the address is too long and how would seo be affected or improved

My domain : CreditCardPaymentGateways dot in  even after 6 months is not ranking well. Could it be due to length of it?  Also I've blocked backlinks to some directories( without nofollow) using robots.txt.  I suspect either is playing spoilsport in good rankings of my site, which I've optimized well and has least competition.


What's the difference between using \sl and \slshape? I don't see any in the pdf.

I understand that \bf and \it are now obsolete in LaTeX and that \textbf and \textit are proper, as they produce more sophisticated (in particular, cumulative and properly kerned) changes to font style. I have read the  and I understand the rules and their reasons, as well as the several other commands that are affected.  However, I find it convenient to use LaTeX for notetaking during lectures, and in that rushed environment, shortening a command by any number of keystrokes helps keep me from falling behind. \bf and its two-letter kin are still very useful to me for that reason, and once a presentation is finished I can go through and replace all appearances of \bf et al. with \textbf et al.  My question is this: is there a plan eventually to replace the short font style commands like \bf with the implementations of \textbf etc. some day, or should I expect \bf always to remain in existence but obsolete, for reasons of backward compatibility with original TeX? Original TeX has been greatly improved on in countless ways, but in the heat of transcription I sometimes miss its conciseness.


You don't get to see your sister cry.  Why don't you conjugate the verb cry (...your sister cries)? Is it because is it the second verb (if that's the case, what is that rule called?) or is there another reason? Does it have something to do with the sister being subject form? I know this is quite a dumb question but I couldn't find anything on Google. I know that it should be "cry" and not "cries" (I can hear that that's correct) but I can't motivate why.

This question has been bothering me for a while. It came up when I was reading Chapter 16 of "A Comprehensive Grammar of the English Language."   How to explain the grammatical structure of the following four sentences?    "We knew him to be a spy." "I saw her leave the room." "I heard someone shouting." "I got the watch repaired."    What category do the four non-finite clauses in boldface fall into? They do not seem to fall into any of relative, nominal, comparative and adverbial clauses.


I installed windows 7 many months ago on my laptop, and I don't exactly remember, which method I followed for installation : whether clean Install or startup repair. I find memory shortage and when I searched for items to delete, I found a folder named "windows.old", which is 44 GB fat. Can I delete this folder, if it is of no use for current windows ?

I've just changed my laptop OS from Windows Vista to Windows 7.  I didn't choose to have both OS together, I just want to have Windows 7.   I was specting Windows 7 instalation program to format/clean my HD and leave me most of its capacity for a fresh start. But I've found, once the OS has been isntalled, that all files and programs from the Vista era are still in my HD, in a folder called Windows.old   I don't need these programs and files, I want to have as much HD space as possible and Windows 7 as clean as possible, what should I do?  Can I just delete Windows.old folder? Would that affect the how Windows 7 works?  Maybe is because I ended up angry with Vista, but I don't like the fact that there wasn't any cleaning/formatting ..   Thanks a lot


If we consider the sequence $a_n = (n-1)!$ then the Gamma function $\Gamma(n)$ gives exactly $a_n$ at each positive integer $n$. Let $F_n$ denote $n^{th}$ Fibonacci number. Does there exist a continous function $F(x)$ such that $F(n) = F_n$ at each positive integer $n$? If it exists should it be unique ?

How is a continuous Fibonacci number $F_n$ defined? (like the Gamma function for factorials) Tried with Binet's formula (Wiki) , but to no luck. F[n_] = N[GoldenRatio^n - 1/GoldenRatio^n]/Sqrt[5] Plot[F[n], {n, 3., 12.}, GridLines -> Automatic] FibonRatio[n_] = N[Fibonacci[n + 1]/Fibonacci[n]]; Plot[{FibonRatio[n], N[GoldenRatio], 1.7}, {n, 3., 12.},   GridLines -> Automatic]  Also using this continuous function definition how is it proved that $$\lim _{n\rightarrow \infty}\dfrac{F_{n+1}}{F_n} = \phi$$ ( where $\phi$ is the GoldenRatio) ? Appreciate your comments.


I tried the android app and so far I don't see any bugs etc, maybe one crash but I miss button for saving questions.  If this is multiple "question" I apologize for spamming. Would you please add it? Thank you.

I've found an interesting question when browsing Freelancers.SE. I've tried to star (favorite) the question but I couldn't find the option...  How to star a question from the Android app?


I have been trying to make a udev rule for a while, but without succes. For testing purposes, I have a file /etc/udev/rules.d/80-power.rules which contains  ACTION=="add", RUN+="/opt/eigen_scripts/waarschuwing_stroomkabel.sh"   Supposedly, this should run the specified script whenever a device like a USB stick is added (I monitored udevadm and the action indeed is add when plugging in a USB stick). This is not actually what I want to achieve in the end, but it seemed like the easiest way to at least get some kind of udev rule working. If you think the problem lies here, feel free to suggest an even simpler rule, I'd be glad to get any rule at all working.  The script in /opt/eigen_scripts/waarschuwing_stroomkabel.sh is  notify-send -i face-worried "Geen stroom!" "Sluit de adapter aan of de computer valt misschien uit."   and should send a notification.  Both files mentioned can be read and executed by root and all users. Using bash I have manually run the script in the second file (both as root and as normal user) and it works just fine. I have rebooted the system several times. I don't know what to try anymore. Thank you for your help.  I am working on a laptop with Ubuntu 16.04 installed.  Update: I have been looking at the duplicate question and the links in the comments, but haven't gotten much wiser. Updating my script to the script  #!/bin/bash  export DISPLAY=":0" notify-send "device plugged"   and rebooting did not solve anything, while it did at least partially work for the dupplicate questions's OP. I tried to follow the steps in the first two answers of  but without effect. And I do not understand what  is even about.

I use Linux Mint 13 MATE, and I'm trying to set up notifications when I plug/unplug devices.  First of all, I found  package, but unfortunately it almost doesn't work for me: it works for very little time (1-2 minutes), and then, if I connect/disconnect any device, it crashes:  Traceback (most recent call last):   File "./udev-notify.py", line 319, in <module>     notification.show() glib.GError: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name :1.1061 was not provided by any .service files   I haven't found any solution, so I had to remove it. (filed  also)  Surprizingly, there're no similar utilities I've found so far. Then I tried to write udev rules that should match all devices. I have added new file /etc/udev/rules.d/notify.rules :  ACTION=="add",    RUN+="/bin/bash /home/dimon/tmp/device_plug.sh" ACTION=="remove", RUN+="/bin/bash /home/dimon/tmp/device_unplug.sh"   And two scripts:  device_plug.sh:  #!/bin/bash  export DISPLAY=":0" notify-send "device plugged"  /usr/bin/play -q /path/to/plug_sound.wav &   device_unplug.sh:  #!/bin/bash  export DISPLAY=":0" notify-send "device unplugged"  /usr/bin/play -q /path/to/unplug_sound.wav &   It works, but it works very dumb. My questions are:   How to get actual title of the device attached, the same as I can see in lsusb output? Currently, I just got notifications like "plugged" and "unpugged", and I can't find how can I retrieve the name of the device in my udev rule (If I can, then I'd pass it to my script as a parameter) Currently, too many notifications are activated. Say, when I attach my USB stick, I got about 15 notifications! But, if I run lsusb, attached USB stick is displayed as just single device. So, it seems I should add some more argument to rule filter, but I can't find it out. Probably there's some better solution for device plug/unplug notifications? Please suggest if you know something.


It says "loadout not available - no connection to Steam"...what? What does this mean? I'm pretty sure I'm connected to Steam.

Occasionally I will get a message from TF2 about being unable to connect to the item server, and I will be stuck with a pure stock loadout.  What is strange is everyone else on the same server will have all of their items.  How can I restore the item server connection?  It must be a problem on my end - if the item server were down, everyone else should be using stock loadouts with no hats as well.  Note: I know about the heartbeat console command.  That is for servers, not clients and does nothing for me.


I am relatively new to Linux and Ubuntu. I have attached the system monitor to the bar (the upper bar of the screen) and opened the preference to configure this gadget. On the processor tab I see that I can mark the choose 5 colors : user, system, nice, IOwait and idle. I can understand all 4 (I think...) except for "nice". What is this "nice" ? I read  and I understand that the superuser can perform tasks with greater priority but , what does it mean if I see it in the system monitor without me running any new nice processes ?

What does the 'Nice' column represent on the processes tab of the system monitor?


As stated in the description for the  cantrip (PHB, p. 282), the caster makes a "melee spell attack" against the target.  You create a long, vine-like whip covered in thorns that lashes out at your command toward a creature in range. Make a melee spell attack against the target.  The third benefit of the  feat says (PHB, p. 168):  When you make a melee attack against a creature, you don’t provoke opportunity attacks from that creature for the rest of the turn, whether you hit or not.  Given that the third benefit of the Mobile feat only requires a melee attack to be made to avoid provoking opportunity attacks (without specifying the type of melee attack), would that cantrip fulfill the trigger for Mobile? In other words: Is a spell melee attack considered a "melee attack" for the purpose of the Mobile feat?

The  spell says:     The spell captures some of the incoming energy, lessening its effect on you and storing it for your next melee attack. You have resistance to the triggering damage type until the start of your next turn. Also, the fist time you hit with a melee attack on your next turn, the target takes an extra 1d6 damage of the triggering type, and the spell ends.   The  cantrip says:     Lightning springs from your hand to deliver a shock to a creature you try to touch. Make a melee spell attack against the target. You have advantage on the attack roll if the target is wearing armor made of metal. On a hit, the target takes 1d8 lightning damage, and it can’t take reactions until the start of its next turn.   If I absorb fire damage with absorb elements, would I be able to add an extra 1d6 fire damage to my next shocking grasp attack?


I need a command that acts like tail -f (displays file changes in realtime), but it should display the new output for all files (even if the new file is created/added). I don't know what files will be there in the directory I need to listen, that's why I need it.  I found out that tail -f folder_name/* does what I want, but it doesn't work if I'll add a new file, it wouldn't display its changes.  Is there a way to accomplish what I need?

I normally  watch many logs in a directory doing tail -f directory/*. The problem is that a new log is created after that, it will not show in the screen (because * was expanded already).  Is there a way to monitor every file in a directory, even those that are created after the process has started?


I'm getting a List of object A, then I use Apache Commons Collection4 to transform the obtained List from having A instances to having B instances.      listOfBs = (List<B>) CollectionUtils.collect(listOfAs, componentTransformer);   However, eventually I need to have an Array of Bs not a List.  So my question is, which is faster.   Convert the list using CollectionUtils.collect Create an array using listOfBs.toArray(new B[listOfBs.size()])   Or   Loop over the listOfAs Transform each A object to a B object Add each B object to an array (B[])   The difference between the first approach and the second approach is that the first approach has much less code, but I'm not sure if the toArray method bares a hidden loop or expensive operations.  What I see in the second approach is that I'm sure I'll loop only once over the listOfAs list.  So which approach is faster ?

Assuming I have an ArrayList  ArrayList<MyClass> myList;   And I want to call toArray, is there a performance reason to use  MyClass[] arr = myList.toArray(new MyClass[myList.size()]);   over  MyClass[] arr = myList.toArray(new MyClass[0]);   ?  I prefer the second style, since it's less verbose, and I assumed that the compiler will make sure the empty array doesn't really get created, but I've been wondering if that's true.  Of course, in 99% of the cases it doesn't make a difference one way or the other, but I'd like to keep a consistent style between my normal code and my optimized inner loops...


I am using tmux 2.1 on Ubuntu 16.04.  I would like to have the background have some transparency.  A lot of times I need to reference something at the same time I use the terminal.    I have looked at   and   this seemed to suggest that setting bg=default would do it but it gives me the default solid purple. I tried using a hex code of #80FFFFFF which tmux rejected.  edit: The old post noted above does not explain how to set the transparency in tmux- at least not to me :(  Help greatly appreciated.

I recently set up  and noticed that the background color on the status-left, if changed, refuses to go back to default and transparent (if transparency is enabled).  I was able to fix the status-right (because it's before the background is changed), but it seems impossible to clear/erase the background after it's set for a section. I'd love to be wrong about this, though, and was wondering if anyone knows of a solution? set -g status-left='#[bg=colour89]ANYTHING CAN GO HERE[#bg=default] AND HERE TOO!' I'd expect to have the background cleared out (bg=default at the beginning would have it stay transparent, and works for status-right), but I get a dark grey instead. TERM = screen-256


A few days ago, my TexStudio (which I have used without difficulty for years) started being slow compiling, not compiling when I hit the "build and view" and "build buttons", and saving these strange extra files when it finally does go through. Again, these are not the usual extra files, like the ".aux" file. They look like maybe they are failed save attempts. It is doing this for every project I work on, even old ones I pull up that have pretty different preambles. Here are examples:  Cover Letter Template 1.tex.b10756 Cover Letter Template 1.tex.r10756  Anyone know what has gone wrong, and how I can fix it? I've had no luck searching for other people having this problem, or from any other help source.

I need to compile between two and four times before I see changes I make in the editor (TeXstudio) and each time I compile, a new .tex file is created with random letters and numbers at the end.   For example, If I create the file hello.tex and compile two to four times I'll get the file,   hello.tex.QU6664      then I make some small changes in the editor and compile two to four times I'll get the additional file,   hello.tex.Ak6664   After continuing to do this (each time compiling between two to four times before I see the changes I made), I now have many files that look like  hello.tex.QU6664, hello.tex.Ak6664, hello.tex.YX6664, hello.tex.sN6664, hello.tex.Ss6664, ...   A little bit of additional information (in case it's relevant): Everything was working fine up until a few days ago, i.e. only needed to compile once and only the file hello.tex was created. I still only get one .aux,  .synctex and .pdf files. I use TeXstudio to write and compile. I don't think it has anything to do with the bibliography (I tried removing bibliography altogether and still having the same problem).  How do I prevent these additional files from appearing and only compiling once like I used to? Has anyone had a similar problem?


I have an issue using python Flask-RESTful. Consider the code below:    Class ServiceAPI(Resource):     def post(self):         return 'Hello, World!', 200   Then the client receives:    "Hello, World!"       instead of    Hello, World!   the extra double quotes are undesired. How can I avoid them? I don't want to solve the issue by stripping/trimming the data received, in the client.

Given a string of JSON data, how can I safely turn that string into a JavaScript object?  Obviously I can do this unsafely with something like:  var obj = eval("(" + json + ')');   but that leaves me vulnerable to the JSON string containing other code, which it seems very dangerous to simply eval.


Equation of circles of radius $r$ :-  $$ {( x-a)}^2 +{(y - b)^2} = r^2 $$  Then I treated $a,b,r$ as arbitrary constants .  And differentiated the equation thrice .  which gave the wrong result   As in the solution in the book equation was differentiated twice .     So why do we not treat $r$ as arbitrary constant and differentiate it twice ?   My question is very different from "" as this question is aking what to do whereas i am asking why do not we take radius as arbitrary.

Can someone please post a detailed step-by-step procedure. Given the circle with a radius a, what is the differential equation of the circle.


I'm trying to make an object follow a path from a recording, and I'd like to do it with the motion tracker. I'm not trying to solve camera motion, just the object. I've got a tracker in the motion tracker, but I can't figure out how to make it an empty in the 3d space. (of course, it'll only move in two dimensions.)

I am using Ubuntu 15.04 and Blender 2.72b.  I've got a video clip where I want to display some annotation-like text next to some potatoes on a white table. The potatoes move a little in the video so I would need to adjust the text a bit every few frames.  (I am a total beginner, I have not used Blender's clip editor before.)  How would I attach text to a tracked point (to the potato) and manually adjust the text's location when required?


Solve   $$ \int\frac{dx}{(1+x^4)^{1/4}} $$   Set $t=\log x\implies x=e^t\implies dt=\dfrac{dx}{x}$ $$ \int\frac{dx}{(1+x^4)^{1/4}}=\int\frac{\dfrac{1}{x}dx}{\big(\dfrac{1}{x^4}+1\big)^{1/4}}=\int\frac{dt}{(e^{-4t}+1)^{1/4}} $$ Set $e^{-4t}+1=y\implies-4e^{-4t}dt=dy$ $$ I=\int\frac{e^{-4t}\,dt}{e^{-4t}(e^{-4t}+1)^{1/4}} = \frac{-1}{4}\int\frac{dy}{(y-1) y^{1/4}} $$  The solution given in my reference is $$\frac{1}{2} \left(\dfrac{1}{2}\log\dfrac{1+z}{1-z}-\tan^{-1}z\right),\quad z=\frac{(1+x^4)^{1/4}}{x}$$  How do I see what substitution to choose in order to find such a solution ?

How can I solve integral of types  (1) $\displaystyle \int\dfrac{1}{\sqrt[4]{x^4+1}}dx$  (2) $\displaystyle \int\dfrac{1}{\sqrt[4]{x^4-1}}dx$


Problem:     Let $f$ be a real valued continuous function on $\mathbb{R}$ . Suppose that    $$f(x+y) + f(x-y) = 2[f(x)+f(y)]$$   for any $x,y\in \mathbb{R}$. Show that there exists $\alpha$ such that $f(x) = \alpha x^2$ for all $x\in \mathbb{R}$.    My attempt: Frankly, I'm not really sure where to begin. I can rewrite the problem as  $$\frac{f(x+y) + f(x-y)}{f(x)+f(y)} = 2$$  which looks a little bit like the Lipschitz condition. Also, it seems like a clever substitution is going to happend with $f(x-y)$ and $f(x+y)$. Beyond that I can't really get a hold on the problem. Any hints or suggestions?

Find all the functions $f\colon\mathbb{Q} \to \mathbb{Q}$ such that $f(x+y) + f(x-y) = 2f(x) + 2f(y)$, for all rationals $x,y$.


I am in Ubuntu 12.04.  When I install the software updates with "Update Manager", there is a pop up dialog which tells me "The volume "boot" has only 0 byte disk space remaining"  My current kernal in use is:  myname: ~$ uname -r 3.11.0-19-generic   The content of boot folder is:  Laptop1:~$ ls -lah /boot total 215M drwxr-xr-x  4 root root 2,0K abr 26 14:49 . drwxr-xr-x 23 root root 4,0K abr 26 14:48 .. -rw-r--r--  1 root root 983K oct 23  2013 abi-3.11.0-13-generic -rw-r--r--  1 root root 983K nov 12 18:33 abi-3.11.0-14-generic -rw-r--r--  1 root root 983K ene 30 18:53 abi-3.11.0-15-generic -rw-r--r--  1 root root 984K feb  3 23:20 abi-3.11.0-17-generic -rw-r--r--  1 root root 985K mar 11 20:06 abi-3.11.0-19-generic -rw-r--r--  1 root root 985K abr  1 23:08 abi-3.11.0-20-generic -rw-r--r--  1 root root 160K oct 23  2013 config-3.11.0-13-generic -rw-r--r--  1 root root 160K nov 12 18:33 config-3.11.0-14-generic -rw-r--r--  1 root root 160K ene 30 18:53 config-3.11.0-15-generic -rw-r--r--  1 root root 160K feb  3 23:20 config-3.11.0-17-generic -rw-r--r--  1 root root 160K mar 11 20:06 config-3.11.0-19-generic -rw-r--r--  1 root root 160K abr  1 23:08 config-3.11.0-20-generic drwxr-xr-x  5 root root 1,0K abr 26 14:48 grub -rw-r--r--  1 root root  26M nov 23 17:56 initrd.img-3.11.0-13-generic -rw-r--r--  1 root root  26M dic 24 14:55 initrd.img-3.11.0-14-generic -rw-r--r--  1 root root  26M feb  1 20:46 initrd.img-3.11.0-15-generic -rw-r--r--  1 root root  26M feb 22 14:00 initrd.img-3.11.0-17-generic -rw-r--r--  1 root root  26M abr 22 20:57 initrd.img-3.11.0-19-generic -rw-r--r--  1 root root  26M abr 26 14:48 initrd.img-3.11.0-20-generic drwx------  2 root root  12K oct 30 21:03 lost+found -rw-r--r--  1 root root 173K jun 17  2013 memtest86+.bin -rw-r--r--  1 root root 175K jun 17  2013 memtest86+_multiboot.bin -rw-------  1 root root 3,2M oct 23  2013 System.map-3.11.0-13-generic -rw-------  1 root root 3,2M nov 12 18:33 System.map-3.11.0-14-generic -rw-------  1 root root 3,2M ene 30 18:53 System.map-3.11.0-15-generic -rw-------  1 root root 3,2M feb  3 23:20 System.map-3.11.0-17-generic -rw-------  1 root root 3,2M mar 11 20:06 System.map-3.11.0-19-generic -rw-------  1 root root 3,2M abr  1 23:08 System.map-3.11.0-20-generic -rw-------  1 root root 5,4M oct 23  2013 vmlinuz-3.11.0-13-generic -rw-------  1 root root 5,4M nov 12 18:33 vmlinuz-3.11.0-14-generic -rw-------  1 root root 5,4M ene 30 18:53 vmlinuz-3.11.0-15-generic -rw-------  1 root root 5,4M feb  3 23:20 vmlinuz-3.11.0-17-generic -rw-------  1 root root 5,4M mar 11 20:06 vmlinuz-3.11.0-19-generic -rw-------  1 root root 5,4M abr  1 23:08 vmlinuz-3.11.0-20-generic   Questions:  Among those files in boot folder, which can be removed?  Thank you:)

After a recent update, I'm getting an alert saying:  The volume boot has only 0 bytes disk space remaining   But my computer has plenty of HD space free. Does anyone know how I resolve this. (If it's relevant, I'm using the whole disk encryption feature of the alternate install image for Ubuntu 12.04).


I was willing to buy a Dell XPS 13 2 in 1 (model 9310) but the seller told me that it is not compatible with Ubuntu. Could anybody confirm? Thanks.

I have a device on which I would like to install Ubuntu. How do I find out if Ubuntu will work on it?


So, Im playing Terraria, I recently defeated all mechanical bosses: The Destroyer, The Twins and Skeletron Prime. Ive gone to the jungle and got myself a full set of Chlorophyte and Im confused. What do I do next? (Im on PC by the way)

I'm kind of stuck in Terraria. I have full silver armor and 12 hearts (gold/silver gear).  I have just killed the Eye of Cthulhu.  I was thinking about gathering gold armor, but gold is damn scarce. I have tried searching for floating islands (at 406 altitude) but if I go to far I get attacked by Harpies, and I can't build a sky bridge and fight them at the same time.  My meteorite landed in corruption and it's impossible to collect it (I get swarmed by meteor heads with no way to run).  So what is the most natural progression? Should I try and find gold (where?), try to kill the Eater of Worlds, try to mine meteorite or try to fight off imps and collect some hellstone?


could you please help me find the error in my logic? The function doesn't work well and I can't figure out why. The instructions are: Write a function remove_duplicates that takes in a list and removes elements of the list that are the same. Do not modify the list you take as input! Instead, return a new list. For example: remove_duplicates([1,1,2,2]) should return [1,2].  For [1, 2, 2, 5, 5, 5, 7, 7] I'm getting this output [1, 2, 5, 7], which is good. However, for [4, 9, 9, 4] the output is [9, 9, 4], which is wrong. I can't find out what the problem is. I started learning programming a few weeks ago, so I'm a novice. Thanks!  My code:  def remove_duplicates(l):     nl = list(l)     i = 0         while i <= len(nl)-2:         j = i + 1         while j <= len(nl)-1:             if nl[i] == nl[j]:                 nl.remove(nl[j])             else:                 j += 1         i += 1     return nl

Is there a built-in that removes duplicates from list in Python, whilst preserving order? I know that I can use a set to remove duplicates, but that destroys the original order. I also know that I can roll my own like this:  def uniq(input):   output = []   for x in input:     if x not in output:       output.append(x)   return output   (Thanks to  for that .)  But I'd like to avail myself of a built-in or a more Pythonic idiom if possible.  Related question:


The Software Center closes instantly after I opened it. sudo apt-get update and all commands related to this don't work either.   E: Typ »!DOCTYPE« in line 1 of sources list /etc/apt/sources.list.d>/medibuntu.list is unknown. E: The sources list could not be read.   Sorry that its German but language selection doesn't work as well. It seems like the lists can't be opened :(

There is a glitch on the Ubuntu Software Center and whenever I open it an error appears and it keeps loading and never opens.  Why does this happen?  I have installed Ubuntu 13.04 on a disk and partitioned it.  Please help me and ask for excess information if you need it.  If you know of any duplicates please show me them!!  I get the following error in a terminal  SystemError: E:Type '<!DOCTYPE' is not known on line 1 in source list /etc/apt/sources.list.d/medibuntu.list   The /etc/apt/sources.list.d/medibuntu.list file contains a HTML document.


for some reasons i can't use PDO so i have created a simple function to clean input data, please view and suggest modification to prevent from SQL and XSS. here is function.  function cleanStr($cStr) {     $cStr = trim($cStr);     $cStr = htmlspecialchars($cStr);     $cStr = addslashes($cStr);     return $cStr; }

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


I am having issues with the rig i generated through rigify. When I hit "generate rig" a rig is created with the "palm" widget turned vertical instead of horizontal. I also cannot rotate any of the widgets in pose mode. The widget highlighted in blue will not move or rotate. The same thing happens with other blue and green widgets in the rig.  The file is located here:  Any help would be greatly appreciated!

I am having the same exact issue as described here:   . I would comment but do not have enough reputation.  A three-fingered character with mis-rotation of the hand IK control. See the attached .blend file. I believe I have setup the metarig with the proper rolls, and changing the roll of the hand or palm bones in the metarig has no affect on the outcome in the generated rig. I believe I have also assigned the correct rig types to the first palm bone as well as each of the fingers. All other controllers/bones seem to generate correctly. I cannot seem to set roll manually in the generated rig either. Is there a workaround?


, it's stated that the condition of $\operatorname{im} T$ being closed in the definition of Fredholm Operator is redundant. Why is that?  Edit: Most proofs use the existence of a closed $N$ such that $T:X\rightarrow Y$, $Y=imT\oplus N$. However, why does such a $N$ exist?

Let $X$ and $Y$ be Banach spaces. A bounded operator $T\colon X\to Y$ is called Fredholm iff   The dimension of $\ker(T)$ is finite, The codimension of the image $\mathrm{im}(T)$ is finite, The image $\mathrm{im}(T)$ is closed in $Y$.   Question: Is the third condition redundant?  Some lecture notes I'm working through claim that the third condition follows from the second one together with the . I've checked some books on functional-analysis without finding a proof of this.


Oh My Zsh has this lovely feature where you can just type dir-name instead of cd dir-name to access the directory called dir-name.  In my old .bashrc I had a function that overwrites the builtin cd function such that every time I would cd into a directory, ls would be called in that directory.  However, this only works if I explicitly call cd dir-name.  Is there a way to do this in Oh My Zsh such that every time I access a directory by typing its name, ls will be called in that directory?

Instead of the normal cd I've created my own function  function cd {     builtin cd "$@" && ls -F }   This works great for when I use commands like cd someDir/subDir but not when I change directories via zsh's auto_cd someDir/subDir.  Is there a way to customize what command gets called for auto_cd?


say we have a multivariate normal distribution with ${\boldsymbol Y} \sim \mathcal{N}(\boldsymbol\mu, \Sigma)$ The conditional expection is $\overline{\boldsymbol\mu}=\boldsymbol\mu_1+\Sigma_{12}{\Sigma_{22}}^{-1}({\boldsymbol a}-\boldsymbol\mu_2)$ Is this saying that for each value of $a$ in a dataset you minus the mean and multiply by the covariance matrices to obtain the conditional expectation or is it a double summation of $ a - \boldsymbol\mu_2$? I am slightly confused as to what the terms actually are and how to calculate them.

We have a multivariate normal vector ${\boldsymbol Y} \sim \mathcal{N}(\boldsymbol\mu, \Sigma)$. Consider partitioning $\boldsymbol\mu$ and ${\boldsymbol Y}$ into  $$\boldsymbol\mu = \begin{bmatrix}  \boldsymbol\mu_1 \\  \boldsymbol\mu_2 \end{bmatrix} $$ $${\boldsymbol Y}=\begin{bmatrix}{\boldsymbol y}_1 \\  {\boldsymbol y}_2 \end{bmatrix}$$  with a similar partition of $\Sigma$ into $$  \begin{bmatrix} \Sigma_{11} & \Sigma_{12}\\ \Sigma_{21} & \Sigma_{22} \end{bmatrix} $$ Then, $({\boldsymbol y}_1|{\boldsymbol y}_2={\boldsymbol a})$, the conditional distribution of the first partition given the second, is  $\mathcal{N}(\overline{\boldsymbol\mu},\overline{\Sigma})$, with mean $$ \overline{\boldsymbol\mu}=\boldsymbol\mu_1+\Sigma_{12}{\Sigma_{22}}^{-1}({\boldsymbol a}-\boldsymbol\mu_2) $$ and covariance matrix $$ \overline{\Sigma}=\Sigma_{11}-\Sigma_{12}{\Sigma_{22}}^{-1}\Sigma_{21}$$  Actually these results are provided in Wikipedia too, but I have no idea how the $\overline{\boldsymbol\mu}$ and $\overline{\Sigma}$ is derived. These results are crucial, since they are important statistical formula for deriving Kalman filters. Would anyone provide me a derivation steps of deriving $\overline{\boldsymbol\mu}$ and $\overline{\Sigma}$ ? Thank you very much!


I have made a Javascript/html game. Now the problem I have is anyone can edit the client code and cheat in game for example there is a man shooting a enemy.    Man HP:          100 Enemy HP:      50     <div id ="man" hp="100" > </div>   Now if someone changes the hp attribute to a very high value then he becomes literally immortal making the game easy.  Now how can I prevent this type of thing ?

I'm planning on venturing on making a single player action rpg in js/html5, and I'd like to prevent cheating. I don't need 100% protection, since it's not going to be a multiplayer game, but I want some level of protection.   So what strategies you suggest beyond minify and obfuscation?  I wouldn't bother to make some server side simple checking, but I don't want to go the Diablo 3 path keeping all my game state changes on the server side.  Since it's going to be a rpg of sorts I came up with the idea of making a stats inspector that checks abrupt changes in their values, but I'm not sure how it consistent and trusty it can be.  What about variables and functions escopes? Working on smaller escopes whenever possible is safer, but it's worth the effort?  Is there anyway for the javascript to self inspect it's text, like in a checksum?   There are browser specific solutions? I wouldn't bother to restrain it for Chrome only in the early builds.


I have to show that $(a+b)^p=a^p+b^p$ in $\mathbb Z/p\mathbb Z$ for $p$ prime. In other word that $p$ divide $\binom{p}{k}$ for $0<k<p$. I tryied many thing but impossible to conclude algebraically. But can I do like this: $$\binom{p}{k}=\frac{p!}{k!(p-k)!}=\frac{(p-k+1)(p-k+2)... (p-1)p}{k!}\in\mathbb N$$ Since $p$ is prime, not in $1\leq i\leq k$ divide $p$ and thus $\frac{(p-k+1)...(p-1)}{k!}\in\mathbb N$ therefore $$\frac{(p-k+1)(p-k+2)... (p-1)p}{k!}=mp$$ for $m\in\mathbb N$ and thus $p$ divide $\binom{p}{k}$.  Do you think it work ? The problem is i'm not sure that (if $m<n$) $$\frac{a_1\cdot ...\cdot a_n}{b_1\cdot ...\cdot b_m}\in\mathbb N\implies \forall a_i, \exists b_j: b_j\mid a_i.$$  What do you think ?

Question : If $p$ is prime, and $0< k< p$ show that $ p \mid {p \choose k}$  ${p \choose k}$ can be rewritten as:  $${p(p-1)(p-2)\dots(p-(k-1))(p-k)! \over (p-k)!\cdot k(k-1)(k-2)\dots3\cdot2\cdot1}$$  Now the $(p-k)!$ cancels out. Since in the numerator we have k consecutive  integers, k divides one of them (not p as p is prime and $k <p$). Then k-1 divides another one or two terms in the k consecutive terms (again not p). This reasoning continues until  3 and 2.   This means that ${p \choose k}$ can be rewritten as pq implying $p | {p \choose k}$  What if any of this proof is wrong. I am worried about any 'overlaps', i.e. say k-6 divides terms that k-3 divides invalidating the argument.  P.S. I hope the above is legible as I am new to this site. Thank you!


I am currently getting a distinct list of data. Properties are MDMMappingCode which is unique and CustNameReporting which can have duplicate data. Data being returned:  From my linq query the data being returned is correct but I only need 1 unique CustNameReporting instead of 5 being repeated. This issue I am facing is the MDMMappingCode is different. What should I change in my linq query to take the first record. Code List<OptionDto> customers = await _appDbContext.MasterDataCustomerActivityGrids                                     .Select(e => new OptionDto() { Value = e.MDMMappingCode, Label = e.CustNameReporting })                                     .Distinct()                                     .OrderBy(e => e.Label)                                     .ToListAsync(cancellationToken);  public class OptionDto {     public string Value { get; set; }     public string Label { get; set; } }

I am playing with LINQ to learn about it, but I can't figure out how to use Distinct when I do not have a simple list (a simple list of integers is pretty easy to do, this is not the question). What I if want to use  on a list of an Object on one or more properties of the object?  Example: If an object is Person, with Property Id. How can I get all Person and use Distinct on them with the property Id of the object?  Person1: Id=1, Name="Test1" Person2: Id=1, Name="Test1" Person3: Id=2, Name="Test2"   How can I get just Person1 and Person3? Is that possible?  If it's not possible with LINQ, what would be the best way to have a list of Person depending on some of its properties in .NET 3.5?


I've imported this word with bounch of flowers. I've thecked the materal, the UV and it looks fine. But somehow, there is this wired "black". And this black even shows up when there is only the World backgroud lighting up the scene. I've tried Blender 2.83 LTS, and 2.9. Some issue. I've tried theck the alpha of the texture image, I've tried change the alpha Clip/Hash/blend. Nothing really helps.... Here's the google drive link the of relavent blender file:

Using v2.73, cycles and a very simple scene: an array of cubes, no big deal.   If I set the shader's material to transparent, the cubes in the foreground do become transparent but those far away in the back do not disappear completely and this strange dark things appear (visible in rendered mode and in final renders)    I've played with the clipping distance on the viewport and camera, but I can't figure out how to make those ghosts go away...


Prove that there exists no Lebesgue-measurable subset $A$ of the real numbers such that for every interval $I$ the Lebesgue measure of $A\cap I$ is half the length of $I$.  My attempt:  assuming there exist such $A$ that works with some interval $I$, I wanted to show that there exists some interval in $I\setminus A$ but I couldn't show it.

In my self-study, I came across the following two interesting, related results:  Let $E$ be Lebesgue measurable, with $\mu(E)>0$ (here $\mu$ denotes the Lebesgue measure). Then:   for any $0<\rho<1$, there exists an open interval $I$ such that $\mu(E \cap I)> \rho \cdot \mu(I)$. In turn we should be able to use (1) with $\rho > 3/4$ to prove that  the set $E-E = \{x-y : x, y \in E\}$ contains an (open) interval centered at $0$ (in particular, if $\rho > 3/4$, the text I am using suggests that $(-\frac{1}{2} \mu(I), \frac{1}{2}\mu(I)) \subseteq E-E$).   I would like to see if anyone visiting today would be up for proving (1) or (2) (inclusive-or). I have tried to work out (1) a few times, but none of my attempts have been satisfactory.


I have been using Cognito Forms for a while now, but when I try to create a new form I am now seeing "powered by cognito forms" at the bottom of my new form.  Is it possible to remove this?

Anyway to remove the “Powered by Cognito Forms” link at the bottom? Sometimes people will accidentally hit that instead of submit and they lose the form and have to fill it out all over again.


I have been refused a Schengen tourist visa reason being the information submitted regarding the justification for the purpose and conditions of the intended stay was not reliable.I don't understand because I provided a cover letter explaining my intention for the trip together with my itinerary.Someone kindly advise what I should do in case I decide to reapply.Thanks.

Schengen refusal formulae can be difficult to understand sometimes.  Sometimes an applicant receives a refusal with:       Justification for the purpose and conditions of the intended stay was not reliable.     often accompanied by:       Your intention to leave the territory of the Member States before the expiry of the visa applied for could not be ascertained.   What is meant by this refusal reason?  What are they trying to say?


My question is the following: how can we prove that singular cohomology groups are homotopy invariants given that singular homology groups are? I am studying this subject, but in the texts I am using there is no mention to this fact.  What properties, if any, of the functor $\text{Hom}$ do we need to prove to get the result? Are there any references that demonstrate this result clearly? In which way do they prove it?  Thanks in advance for your time.  P.S.: I haven't yet been introduced to the Universal Coefficients Theorem, and I would like, if possible, the least expensive and most elementary proof available of this result. And again, thanks for the effort

This is pretty basic, but I can't find any answers on this site on this already. I want to know why the homology of two spaces $X$ and $Y$ are the same when $X$ deformation retracts/is homotopy equivalent to $Y$. I would appreciate an intuitive explanation and a formal proof.  Specifically I'm working through Hatcher's Algebraic Topology (chapter 2.1) and by homology, I mean both simplicial and singular homology as defined in Hatcher.   I also assume this holds for relative and reduced homologies, but if you can explain why that would be great.


So obviously the title says it all. Is this the best way to view my running processes?  ps -u whoami

List all process names for my user.   I could do it with   ps aux | grep username   But the output would be like:  maythux  18343  0.0  0.1 1070868 34504 ?       Sl   Jun03   0:07 empathy maythux  21562  0.0  0.1 703716 32104 ?        Sl   Jun10   0:00 /usr/bin/python /usr/bin/blueman-applet maythux  21574  0.0  0.0  53532  2408 ?        S    Jun10   0:00 /usr/bin/obex-data-server --no-daemon  maythux  25197  0.0  1.0 2199840 258576 ?      Sl   May27   0:24 remmina   But I just want the output look like:  empathy blueman-applet obex-data-serve remmina   So what is the easiest way to do that?


I'm a beginner in PHP, SQL, databases, etc and I'd like to hear people's opinions on whether to use PDO or MySQLi when working with databases, so far I've seen very mixed opinions.  Would you consider somebody who uses MySQLi a professional web developer? Is MySQLi up to industry standards, or is it often disregarded by employers and clients?   I'm sure this question has been asked many times before, but I'd appreciate it if you didn't mark this question as a duplicate, for the reason that I'm looking to get fresh opinions and as many as I possibly can.  Thanks in advance :]

In our place we're split between using mysqli and PDO for stuff like prepared statements and transaction support. Some projects use one, some the other. There is little realistic likelihood of us ever moving to another RDBMS.  I prefer PDO for the single reason that it allows named parameters for prepared statements, and as far as I am aware mysqli does not.  Are there any other pros and cons to choosing one over the other as a standard as we consolidate our projects to use just one approach?


For any business correspondence, I use a graphic, aglogo.jpg.  As long as I'm in the directory where it resides, of course latex always finds it.  But, if I'm working in a different directory it's not found.  Is there a way to make latex find aglogo.jpg no matter what directory I'm in?

I know how to define a package or a class, but how do I make it available (to myself) at all times?  Say I have the package file commonstuff.sty (or myprettyclass.cls), that I want to be able to include in any .tex file I create on my computer. Where do I put it? Do I need to run some installer on it, or is it enough to keep it in a certain folder?  Note: I know I can just place it in the same folder as the .tex file, but that's not what I'm after here. I'm looking for a way to "install" the package centrally on my computer.


For Example: 1.) Women turned Trump’s insulting “Grab’em by the pussy!” into “Pussy Hats” that they sported proudly in The Women’s March. 2.) Trump also attempted to humiliate Hillary Clinton by comments about her pantsuits, and both men and women rallied by founding “The Pantsuit Nation” and by proudly wearing pantsuits to express their support of HRC.

E.g. "geek" or "queer" were originally meant as an insulting term, but were taken by the recipients as titles of pride.   Is there a term for this phenomenon?


The kids are shipped to a different planet to survive for a certain period. I can remember there being a larger kid that had a gun and a dog for protection who ends up dead. In the end, the kids weren't actually shipped off to a different planet, but instead were on Earth the whole time.  I know it is not one of the Heinlein Juveniles books. Can anyone think of anything other than those books?

I would love to identify a sci-fi novel I read in the late 60s or 70s.  It followed a group of young space cadets through their training in the Space Academy.  The training culminated in small groups of cadets being sent through a gateway in the space station, into different worlds where they had to survive whatever conditions they met beyond the gateway, as part of their training.  One such trip went wrong and the group ended up stranded in a hostile world for days, hoping to be rescued by their trainers.  I can't remember much about the story or protagonists so this may be too vague, but I remember descriptions of a vast space station hall and these young cadets bringing whatever kit they hoped they might need - some brought breathing apparatus and full survival gear, but others came with very little as they believed they would not be sent into conditions where they could die without the right equipment.  They hadn't bargained for the power surge or whatever it was that misdirected them as they passed through the gateway!  I also remember rivalry between the cadets - I think the hero was male and quietly heading for top cadet of the year award... and I think at least one of the group died in the unknown planet before they were rescued.  Does this ring a bell with anyone?  I remember the mood and tension more than the details but it was a long time ago!  I have a 10-year old son who I think would love this kind of story.  If anyone can help you have my thanks!


When working in tex files, I follow the rule     One sentence per line   because I think this gives the best diff sets using version control systems (usually mercurial or git) so that one can best see the changes of yourself and others to the file.  Anyway, many of my collaborators follow the rule     break lines after 80 characters   usually because their emacs or vi makes this best to read on screen (and because they are used to do so from the good old days).  I currently believe that, whichever editor people use, it should be possible to have lines displayed however people prefer without introducing newline characters in the source. In particular, one should not force collaborators to also stick to the personally preferred line length by using newline characters.  So my question is:     Are there good reasons for restricting lines to 80 characters when editing tex-files, and introducing newlines to not pass that limit?   This is clearly a soft question and I have not actually checked if this is appropriate to ask here. The reason I do so is that this problem occurs (for me) only when interacting with collaborators on tex files, so I consider it to be very specific to latex collaboration.

Are there any best practices for how long to make your lines in your source file?  I'm also interested if there are best practices for it if there aren't any LaTeX-specific best practices.  I originally typed my LaTeX files like I was in Word:    each paragraph on its own line.   However, I eventually found that to be rather cumbersome and so I switched to one sentence per line (around the same time I moved from Dropbox to git).   That was large improvement for me.  Since I tend to write long sentences and like my footnotes, I tried an experiment in a file:    break lines after commas as well as after periods.   So far, it seems that this method would require a good bit of manual clean-up, since it produces some very short lines and there are still overly-long lines in the file.   What methods have you found to be the best for keeping your source's line lengths reasonable?


class ExeTime { public static void main (String[] args) {      LinkedList<Integer> ll = new LinkedList<Integer>();     ArrayList<Integer> al = new ArrayList<Integer>();      addElement("LinkedList", ll);     addElement("ArrayList", al); }  static void addElement(String type, List listType){     final long startTime = System.currentTimeMillis();      for(int i = 0; i<= 1E5; i++){         listType.add(i);     }     final long endTime = System.currentTimeMillis();     final long timeTaken = endTime - startTime;     System.out.println("Type:::: "+type+" ::timeTaken:: "+timeTaken); }  }   Output for above piece of code is ::::  Type:::: LinkedList ::timeTaken:: 11  Type:::: ArrayList ::timeTaken:: 18  Now if I interchange the call for addElement method then I get the following output::::  Type:::: ArrayList ::timeTaken:: 10  Type:::: LinkedList ::timeTaken:: 16  I fail to understand why the sequence to add integer to a LinkedList and ArrayList change the execution time of the method. I tried the same for removing the elements and the results were OK. Could anyone please help me get to know as why this might be happening only while adding elements...

How do you write (and run) a correct micro-benchmark in Java?  I'm looking for some code samples and comments illustrating various things to think about.  Example: Should the benchmark measure time/iteration or iterations/time, and why?  Related:


In a world of programming, there are number of tools which have purposefully lowercase names: like tmux or sed. When talking about this tools, how does capitalization work?  Do I never capitalize these, even when a sentence starts with these? Do branding rules apply here (like iPhone or eBay)?

Possible Duplicate:         In programming language documentation, it is common for keywords to appear in titles. Assuming that the keyword is strictly lowercase in the language, how should that keyword be capitalized if it is used as the first word in a title?  For example:  int int is used to specify an integer type.  -- or --  Int int is used to specify an integer type.


I know that the formula of probability is the following:  P= FO(favorable outcomes)/PO(possible outcomes)  What I do not understand is what is the number of PO(possible outcomes) ?  If we take into consideration the order of the dice (i,e 2,1 is a different outcome than 1,2)then  there are 36 possible scenarios.  But when we are not interested in the order (in Backgammon game the order is not relevant) there will be only 21 possible scenarios.  In this particular scenario which should be the probability ? 6/36=1/6 or 6/21=2/7 ?

In either case, one coin flip resulted in a head and the other resulted in a tail. Why is {H,T} a different outcome than {T,H}? Is this simply how we've defined an "outcome" in probability?   My main problem with {H,T} being a different outcome than {T,H} is that we apply binomial coefficients (i.e. we count subsets of sets) in some common probability problems. But if we take {H,T} and {T,H} to be different outcomes, then our "sets" are ordered, but sets are by definition unordered...   I feel as though the fact that I'm confused about something so basic means that I am missing something fundamental. Any help or insight whatsoever is greatly appreciated!


I do not recall why I have download.opensuse.org, but I am OK just removing whatever is causing this error:  W: GPG error: http://download.opensuse.org  Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6FE3AE1CC7D68E37   This does not appear to be a duplicate question because the solutions proposed in other similar questions are not working here:  # sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6FE3AE1CC7D68E37 Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.OCmHCQ908W --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys 6FE3AE1CC7D68E37 gpg: requesting key C7D68E37 from hkp server keyserver.ubuntu.com gpgkeys: key 6FE3AE1CC7D68E37 not found on keyserver gpg: no valid OpenPGP data found. gpg: Total number processed: 0   I'm on 12.04

I added some extra repositories with the Software Sources program. But when I reload the package database, I get an error like the following:     W: GPG error:  trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8BAF9A6F   I know I can fix it using apt-key in a terminal, according to the official Ubuntu documentation. But I would have liked to do it graphically. Is there a way to do this without using a terminal?


This is a question about an old question which can be found . I also found an answer to that question by Cegaton, though the instruction in the answer didn't help me, and I suspect that it might have only worked for the older version. So I'm using Blender version 2.78, I enabled the "use alpha" and it still doesn't work in any view, I used Gimp2 for the alpha channel and exported it into png, and imported as a plane using the addon, the plane is still a picture with black opaque background.  Screenshots:  Picture in GIMP2   Exporting the picture as Png   Importing the picture as a plane   Choosing the picture   The plane in object-solid view   The plane in object-texture view   An Image for you to test on:  Please note I am not sure if the alpha channel will stay there if you download it please let me know down in the comments.

I must be missing something here.  I'm doing an extremely simple Import Image as Plane using the AddOn and the imported image has an alpha background but it renders (and even previews in the material preview) as black where the alpha background should be.  When I import, I select Emission & Transparent so the material setup is automatic.  I've read similar issues but people are typically missing the transparent node and connecting the Alpha channel from the image into the Mix Node factor.  But this is all here.  I must be missing something really stupid but I've wasted so much time trying to fix this thing.  Any help would be greatly appreciated.  Not sure if it matters but I'm using 2.74 RC2.  Many thanks!  I created this dummy blend file to test outside my project but problem still exists.  Here is the simple .blend file:


We have a Apache 2.4 web server with a couple of virtual hosts with different certificates.  I have  set up SNI name based virtualhosts : ap.mmm.com and ac.mmm.com, it's working great. All on same IP (172.12.12.1) and same 443 port. The question is : what will happen if client will use IP and not server name to get to the Apache server : I.e will use 172.12.12.1:443 instead of ap.mmm.com ?

It's the following part of a virtual host config that I need further clarification on:  <VirtualHost *:80>   # Admin email, Server Name (domain name), and any aliases   ServerAdmin example@example.com   ServerName  141.29.495.999   ServerAlias example.com ...   This is and example config, similar to what I currently have (I don't have a domain name at the moment).  <VirtualHost *:80> - Allow the following settings for all HTTP requests made on port 80 to IPs that this server can be contacted on. For instance, if the server could be accessed on more than one IP, you could restrict this directive to just one instead of both.  ServerName - If the host part of the HTTP request matches this name, then allow the request. Normally this would be a domain name that maps to an IP, but in this case the HTTP request host must match this IP.  ServerAlias - Alternate names accepted by the server.  The confusing part for me is, in the above scenario, if I set ServerAlias mytestname.com and then made an HTTP request to mytestname.com, there would have to be a DNS record pointing to the server's IP for this to work? In which case, is ServerAlias just basically EXTRA ServerName entries?  Say I had a DNS entry such that foobar.com = 141.29.495.999 but then I had ServerName = 141.29.495.999 and ServerAlias was empty, would that mean that although foobar.com gets resolved to the right IP, because there is no reference to accept foobar.com in ServerName or ServerAlias?  Or something. Man I'm confused.


I am fairly new to ubuntu. I am trying to find a package for the Java JDK to use javac and the other compiler utils included in the JRE.  I cannot however seem to be able to install them (either package not found or not installable).   Any help is appreciated. Thanks.

I am trying to install oracle jdk7 64bit on my computer.   I found this   It uses update-alternative -install to install the JDK which is new to me.   I used to only extract the files and add the jdk location to the PATH environment variable before.   Now it seems that I have to run the following commands more than once if I want to install other executables:  sudo update-alternatives --install "/usr/bin/xx" "xx" "/usr/lib/jvm/jdk1.7.0/bin/xx" 1 sudo chmod a+x /usr/bin/xx   Just like the post said:     N.B. remember - Java JDK has many more executables that you can   similarly install as above. java, javac, javaws are probably the most frequently required.   I think this is rather inflexible. So I want to know what the advantage of using update-alternative to install jdk over other methods is.


When processing experimental data, and calculating an uncertainty value in multiple steps, should intermediary uncertainties be used to a certain number of  or kept to the full precision allowed by the calculator/computer?  I have a number of measured values and their associated uncertainties, and I have processed this data to give me a final value and uncertainty without ever limiting significant figures in either the values or uncertainties at each step. Is this the correct way to go about this?

I'm a little confused as to when to use  for my physics class. For example, I'm asked to find the average speed of a race car that travels around a circular track with a radius of $500~\mathrm{m}$ in $50~\mathrm{s}$.  Would I need to apply the rules of significant figures to this step of the problem? $$ C = 2\pi (1000~\mathrm{m}) = 6283.19 $$  Or do I just need to apply significant figures at this step? $$ \text{Average speed} = \frac{6283.19~\mathrm{m}}{50~\mathrm{s}} = 125.664~\mathrm{m}/\mathrm{s} $$  Should I round $125.664~\mathrm{m}/\mathrm{s}$  to  $130~\mathrm{m}/\mathrm{s}$ since the number with the least amount of significant figures is two?


I'm looking for simple way to fit to an exponential decay with a constant background, so something that looks like:   $y=ae^{-bx}+c$  I have an idea of how to do it without the background. I would just take the log and obtain:   $ln(y)=ln(a)-bx$  And then just use linear algebra to find $ln(a)$ and $b$. I can't seem to do this with the constant background though, because I can't simplify the following:   $ln(y)=ln(ae^{-bx}+c)$  Any ideas?

I'm trying to fit an exponential with noise (which in this case is a constant $c$) like this one  $$ y(x) = \alpha e^{- \alpha x} + c \text{ ,}$$  having $(x_i, y_i)$ values (So $\alpha$ and $c$ are unknown and are the ones that I want to determine). Without the noise I would simply linearize the values and then apply the least squares method, but with the noise I have no idea how to do that. Are there any formulas to do it? Thank you.


I am studying improper integrals as part of a project and have come across this sign: $\asymp$. I was wondering what it meant and why it means: $$\lim_{x \to \infty}\frac{f(x)}{g(x)}=L$$ Any clarification would be greatly appreciation.

I'm reading a  by Andrew Granville on analytic number theory.  On page 22 of the paper, there appears a strange looking symbol, undefined.  I've circled it in red in the screenshot below.    Since it's not defined in the paper, I'm assuming it must be standard notation.   From the context, I'm assuming it means something like "as compared to", or "with reference to", but that's just a guess.  Can anyone identify the symbol, even better explain what it means and/or provide a reference?  Is there a name to speak the symbol?  Thanks in advance.


I checked my rep today and I noticed I was down some points. Somebody has downvoted my question four times within 1 minute:    Is this already serial downvoting? Will it be corrected by a rep-recalculation?

I just noticed that I lost a bunch of points from my reputation score, and I used the "reputation" tab on my user profile page to try and track down the cause.  During my investigation, I noticed there was an unusual event of type "reversal". In the normal place of a question title, it says "voting corrected".     What does this mean, and what caused it?  Did I do something wrong? Why did I lose all of that reputation? Is the system punishing me for leaving too many good answers?  Is there any way to earn it back?


I am trying to write an equation that looks like this, everything should be left aligned on the right hand side.     I am using the following code to write this equation.    \begin{equation}   D_{it} = \Bigg\{if \ bank \ i \ issues \ ABS \ at \ time \ t \\   2 \ if \ bank \ i \ issue \ CBs \ at \ time \ t \\    \ 0 \ otherwise   \end{equation}   I am putting \\ for a new line but it does not work. Please guide how I can write the desired equation.

How do I produce a conditional expression with large brackets? For example: X = 0 if a=1, 1 otherwise, with a large left bracket and specifying each condition in a line?


When I type "Students is the type of people you are looking for". Instead of "type of people", it may be something like: "somewhat", "the way to go", etc.. I have my grammar-extension complaining that I should use "are". So I wonder is it really wrong? Could you provide some examples of using plurals with "is"? (it is difficult to search)

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


I'm trying to understand C# and am very confused by this block of code.   Thread thread = new Thread(new ThreadStart(() => {        Thread.Sleep(_rnd.Next(50, 200));        //do other stuff })); thread.Start();   I know a thread is being created and then started but I don't understand the => syntax in this case. From checking other posts on this site, which were hard to find regarding =>, I think it was to do with delegates or that something is being returned? Can anyone shed some light on this? Thanks.

I just came over this syntax in some of the questions in this forum, but Google and any other searchengine tends to block out anything but letters and number in the search so it is impossible to search out "=>".  So can anyone tell me what it is and how it is used?


Let $\mathbb F_{27}$ be the finite field of order $27$. Let $A_{a}=\{1,1+a,1+a+a^2,\dots\}$. Then which of the following are true?   The number of $a\in\mathbb F_{27}$ such that $\operatorname{card}(A_{a})=26$ equals to $12$. $0 \in A_{a} \iff a$ is nonzero. $\operatorname{card}(A_1)=27$ $\bigcap A_{a}$ is a singleton.   For 2 one way is very obvious. If $0=a$ then $0=1+a+a^2+... +a^k$ for some $k <= 27$.Put a=0 and we get $1=0$, which is a contradiction. For the other way round I am unable to proceed.  For 4 I have no ideas how to proceed.

Let $\mathbb{F}_{27}$ denote the finite field of size 27. For each $\alpha\in\mathbb{F}_{27}$ , define $ A_{\alpha}$ $=$ { $ 1, 1+\alpha , 1+\alpha+{\alpha}^2 , 1+\alpha+{\alpha}^2+{\alpha}^3 , .... $} . Then  prove that  the number of  $\alpha\in\mathbb{F}_{27}$ such that $|A_\alpha|$=26 equals 12.  $ 0\in A_\alpha $ if and only if $\alpha\neq 0$ For the first proof , the multiplicative group of the field $\mathbb{F}_{27}$ is cyclic and its order is 26  , so there are 12 generators in that group.   Now  I need  to  show  that  $ 1+\alpha+{\alpha}^2+.. {\alpha}^{25} $ =0  , where order of $\alpha$=26 . Since   $\alpha ^{26}$ =1 ($\alpha$-1)(1+$\alpha$+${\alpha}^2$+...+${\alpha}^{25}$)=0 , since $\alpha\neq 1$  , So $ 1+\alpha+...+{\alpha}^{25} $ =0 My question is , can I write these last two  lines?  I mean are those two lines alright to write? If those two lines are invalid then I need some help to show  $ 1+\alpha+{\alpha}^2+..+{\alpha}^{25} $=0  .Thanks


Objects in my sample have multiple dimensions. Some dimensions are measured in kilometers and some in kilograms, there are also categorical variables that I need to quantify. I am planning to use weighted Euclidean distance in cluster analysis. My question is: Should I standardized (subtract mean and divide by standard deviation) each dimension before studying clustering?

When running hierarchical clustering analysis of a matrix of individuals x samples (e.g., employee performances across different days), there are several possibilities for normalization. If one is clustering the columns (to see whether on certain days individuals perform similarly), one could   z-score normalize across the rows to make each individual employees mean and standard deviation comparable across days, or z-score normalize across the columns to make all employees comparable within a day, or  not normalize at all and cluster the raw values   Could someone explain the relative advantages/disadvantages of each approach here? To clarify, I am using correlation distance.  Methods 1 or 2 in practice give different results but it's not clear that for the task of seeing if days cluster together, whether #1 or #2 are more appropriate if one chooses to normalize.


I am doing some threading. In the postExecute I need to perform an iterator task. I check if the iterator() is null, but it's still producing this error:  java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.List.iterator()' on a null object reference         at co.appname.app.Fragments.F_EditPhoto$FiltersAsyncTask.onPostExecute(F_EditPhoto.java:772)   Here is my code, Im checking for what I think is every possible null scenario. Can you advise what I am doing wrong?  @Override         protected void onPostExecute(Void aVoid)         {             List<K_FilterPreview> filtersCache = _positionToFiltersCacheMap.get(_selectedEditImage.position);             if (filtersCache == null || filtersCache.iterator() == null)             {                 System.err.println("Filter cache was null");             }              // THIS IS THE LINE THROWING THE ERROR!             Iterator<K_FilterPreview> i = filtersCache.iterator();             while (i.hasNext())             {                 //Do stuff             }         }   This only occurs if I try to start this event as soon as the current event is done processing. If I wait a few seconds before invoking this it works fine. So there is something going on with the threading but I'm not sure what.

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?


Is there a way to remove an upvote/downvote without reversing the vote?

Is there a way to undo when voting up (or down)?  If not, it would be useful.


My website releated to entertainment and movies trailer and review based site, my site viewers list actually very low, I have set keywords which is found from google keywords planner. And created sitemap. Right after my site improvements not good, may I need any changes according to my site traffic and viewers increments.

What are the best ways to improve a site's position in the Google search results?


I have a table in which there is one column, EnteredDateTime. This column contains the date and time. How do I get only the date instead of the date and time?

SELECT GETDATE()   Returns: 2008-09-22 15:24:13.790  I want that date part without the time part: 2008-09-22 00:00:00.000  How can I get that?


I know that, for grid search algorithm, the computational cost of the grid search algorithm would be $O(v^p)$ optimizing $p$ parameters each of which can take on $v$ values, then the computational cost of the grid search algorithm would be $O(v^p)$. But I am not sure what is the computational cost for conducting random walk algorithm. Would it be simply $O(p)$? Thank you,

I am interested in comparing the computational cost of grid search vs. random search algorithm for hyperparameter tuning. Is random search computationally less expensive then grid search? Is there an article/paper that talks about this topic? Thank you,


Is there any difference between MOSFETs with a diode in their symbol and the HEXFET?   Also, is there a difference between MOSFETs with a diode in their symbol and other MOSFETs?

I have noticed that a MOSFET symbol has a little diode in it (or at least what looks like a diode). Does this mean I do not have to worry about using a diode in a circuit that runs a motor using one? I would have used a diode in order to prevent reverse voltage from turning the motor by hand.


Ubuntu 12.10 is not  since May 2014.  Why is there no archived version at  ?

According to this  question, EOL releases are archived to .  But currently, I cannot see Ubuntu 12.10 and Ubuntu 13.04 to be available on this website, while all others(since 4.10) are available, as you can see in the screenshot below    So has canonical and/or Ubuntu devel-teams decided not to archive EOL releases any more? or is it work to be done?


What does  {} \;   string mean in bash?  I've seen it a couple of times, for example, to find and delete all files by name one must execute  find . -name "FILE-TO-FIND" -exec rm -rf {} \;   What does this string do?

Sometimes I see the following command:   find . -name  * -exec ls -a {} \;   I was asked to execute this.  What does {} \; mean here?


I am interested in running a bash script which starts an application (in this case VLC), run it for a certain amount of time and then stop it. I can get this application to start just fine, but it will not stop, using this script:  #!/usr/bin/bash vlc -vvv http://10.0.0.113:8000/stream.mjpg --sout="#std{access=file,mux=ogg,dst=/home/whsrobotics/vlc_project/first_try.mp4}" sleep 10 killall vlc   Not only does it not stop the stream recording, but the app seems to freeze sometimes after I hit Ctrl+Z.  Any suggestions are appreciated.

If and How is it possible to, in Terminal, to get an application to run for 30 seconds, before being force closed, and echoing the logs of that process?


I have a sum  $$\sum_{n} = 1+x+2x^2+3x^3+...+nx^n$$ and asked to simplify it and given $|x|<1$ determine the limit as $n \to \infty$  My first impression is that this is a simple geometric series but I have a mental block as to what is the common ratio. I assume that it was simply $\sum_{n=0}^\infty nx^n$ but when I plug in values to test it the first terms don't seem intuitive. But following from this would the common ratio be x.

How can I evaluate $$\sum_{n=1}^\infty\frac{2n}{3^{n+1}}$$? I know the answer thanks to , but I'm more concerned with how I can derive that answer. It cites tests to prove that it is convergent, but my class has never learned these before. So I feel that there must be a simpler method.  In general, how can I evaluate $$\sum_{n=0}^\infty (n+1)x^n?$$


I just wonder if there is a command line tool for eclipse java file formatter. Or if there is an ant task to execute it.  In my scenario, there are 2 java formatters, one is for android formatter, the other is our internal formatter.  So we have to change it between these two formatter.

Is there a way to use the formatter that comes with eclipse, outside of eclipse?  I would like to format some java files using my formatter.xml file that I have configured using eclipse.  Does anyone have any code examples that would allow me to do this?  I would also like to use this standalone, so the specific jars that are used would be nice.


I just wanted to ask if there is a section for the Persian language OR if there isn't one, do you have any plan on creating such a section?  Because I saw most of Persian questions asked on "English.stackexchange", and I did not find such a specific place for that.

I would like to see a Persian/Farsi language site included within the Stack Exchange world. How likely is this? Is it already being considered?


I have setup my site on Digital Ocean and point the Domain name "A" record to the Droplet IP.  Emails sent by the site are being received in Gmail and other email clients ( SPAM Folder ) but it does not reach at all to outlook.com / hotmail.com email address.  I understand that i have only changed the "A" and "WWW" record of the domain name and now i am sending emails from the droplet, which is somehow not right. What configuration i need to do on the server so the emails sent from my server are trust worthy.   Header of a test email received in Gmail.  Delivered-To: gtemailtesting@gmail.com Received: by 10.182.105.41 with SMTP id gj9csp336738obb;         Thu, 26 May 2016 01:55:41 -0700 (PDT) X-Received: by 10.194.192.10 with SMTP id hc10mr8173424wjc.71.1464252941808;         Thu, 26 May 2016 01:55:41 -0700 (PDT) Return-Path: <register@riyali.com> Received: from riyal.com ([46.101.217.71])         by mx.google.com with ESMTP id wp4si16915971wjb.173.2016.05.26.01.55.41         for <gtemailtesting@gmail.com>;         Thu, 26 May 2016 01:55:41 -0700 (PDT) Received-SPF: neutral (google.com: 46.101.217.71 is neither permitted nor denied by best guess record for domain of register@riyali.com) client-ip=46.101.217.71; Authentication-Results: mx.google.com;        spf=neutral (google.com: 46.101.217.71 is neither permitted nor denied by best guess record for domain of register@riyali.com) smtp.mailfrom=register@riyali.com Received: by riyal.com (Postfix, from userid 1000)     id D27361408BB; Thu, 26 May 2016 04:55:40 -0400 (EDT) To: gtemailtesting@gmail.com Subject: test MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed; delsp=yes Content-Transfer-Encoding: 8Bit X-Mailer: Drupal Sender: register@riyali.com From: register@riyali.com Message-Id: <20160526085540.D27361408BB@riyal.com> Date: Thu, 26 May 2016 04:55:40 -0400 (EDT)  this is a test message   Server Log ( when sent to hotmail):  May 26 05:16:38 riyali postfix/pickup[30639]: E1A1B1408BB: uid=1000 from=<register@riyali.com> May 26 05:16:38 riyali postfix/cleanup[31632]: E1A1B1408BB: message-id=<20160526091638.E1A1B1408BB@riyal.com> May 26 05:16:38 riyali postfix/qmgr[31707]: E1A1B1408BB: from=<register@riyali.com>, size=478, nrcpt=1 (queue active) May 26 05:16:40 riyali postfix/smtp[31634]: E1A1B1408BB: to=<xxx@outlook.com>, relay=mx1.hotmail.com[65.54.188.72]:25, delay=1.2, delays=0.02/0.01/0.53/0.6, dsn=2.0.0, status=sent (250  <20160526091638.E1A1B1408BB@riyal.com> Queued mail for delivery) May 26 05:16:40 riyali postfix/qmgr[31707]: E1A1B1408BB: removed   Server Log ( when sent to gmail ):  May 26 05:25:33 riyali postfix/pickup[30639]: 7D8B91408BB: uid=1000 from=<register@riyali.com> May 26 05:25:33 riyali postfix/cleanup[31719]: 7D8B91408BB: message-id=<20160526092533.7D8B91408BB@riyal.com> May 26 05:25:33 riyali postfix/qmgr[31707]: 7D8B91408BB: from=<register@riyali.com>, size=471, nrcpt=1 (queue active) May 26 05:25:34 riyali postfix/smtp[31721]: 7D8B91408BB: to=<gtemailtesting@gmail.com>, relay=gmail-smtp-in.l.google.com[173.194.65.27]:25, delay=0.84, delays=0.02/0.01/0.35/0.46, dsn=2.0.0, status=sent (250 2.0.0 OK 1464254734 ad7si17051750wjc.239 - gsmtp) May 26 05:25:34 riyali postfix/qmgr[31707]: 7D8B91408BB: removed

This is a  about how to handle email sent from your server being misclassified as spam.  For additional information you may find these similar questions helpful:                    Sometimes I want to send newsletters to my customers. The problem is, that some of the emails get caught as spam messages. Mostly by Outlook at the client (even in my own Outlook 2007).  Now I want to know what should be done to create "good" emails. I know about reverse lookup etc., but (for example), what about a unsubscribe link with an unique ID?  Does that increase a spam rating?


Sorry for the wrong way of title used before.   All sub domains of stackexchange.com have a restriction of "minimum reputations required" for Chat Comment and Image uploading. When members have non-sufficient reputation,    In case of image, if my question does need an image to upload to ask the question specific to topic, and if it is happened to be my first question, or my nth question with below required reputation, I cannot get specific or perfect answers. Images especially of errors, warnings or snapshots of how does the application currently look like(if it is not be explained in words) are prominent among who face those errors before. So by uploading the image they can answer the specific answer. I find no logic in relating reputations with uploading images to ask an efficient question. It will make the new member of this community helpless. In case of comment, some questions or answers need to be clarified slightly different than the questions or answers provided. In this case members with below than required reputations cannot ask a new question just to get small missing information from another answers. In most of the cases the questions asked slightly different than the existing questions will also be considered as duplicate by the forum moderators and members with high reputation. This will lead the member to loose the small reputation that he had before. By opening comment capability to all members irrespective of reputation will enable answerers to update the answer with more information and prevent duplication of questions. When it comes to chat, some domains such as stack overflow restricted a reputation of 50!!. When there is no facility to send personal messages to the members of community, to contact the member for getting additional information about the comment or answer they have posted or to make them know that someone is trying to reach them, is only possible by leaving a msg through chat. for eg: In  post the member GrIsHu has commented to check out the answer provided by him. But there is neither answer posted not link have provided. Now I cannot comment(because of non-sufficient reputation), and I cannot leave a chat msg too(and its a dream to get 50 reputation immediately so that I can enter chat) finally I have no way to ask him the link of the answer he has posted. Even using chat we can get instant help without asking new question.   When members with very high reputation(>50K) use comment to offend each other(In many posts posted on sub domains of stack exchange that I don't like to disclose), new members with <50 reputation who are in hurry or in need of immediate help can't get simple clarifications on answers with high up votes or the required answer in time.  I personally not getting the logic behind restricting newbies to upload an image, use comment for either for clarification or suggestion and restriction on chat to get instant help or use as a means of contacting a particular member.  What is the genuine reason behind these restrictions?

To post an image in a question/answer an user requires at least 10 rep points (see ). To be able to upload an image in the chat, the rep requirements is instead 100 rep point (see ).  Is there any reason to that? I am asking because IF the rationale is to provide more protection inside the chat, the protection is easily circumvented by uploading the image via the question editor, and then copying the link to the chat. Basically, the more restrictive requirement fail to reach its goal - assuming that blocking uploads from new users was indeed the target.  I am not proposing to change that (it doesn't seem worthy the effort) but I was curios to know if this is just a refuse caused by successive changes to the system or if there is actually a different rationale to this that I am missing.  [note: I will remove the double Discussion/Support tag as soon as I can focus if the question has a staff answer - support or will prompt a discussion]


To simplify my problem, I'm gonna start at the source instead of explaining my full-map problem.  I have a shapefile of Ethiopia pulled from GADM (). A lot of the attribute columns are unnecessary and just create extra clunkiness as I perform clips/joins/etc. with the shapefile. So I want to remove all but the first 4 columns. Doing this seems easy enough, and I tried and succeeded with this bit of code:  library(rgdal)  #read in shapefile eth <- readOGR(dsn = "D:/Mapping-R/Ethiopia", layer = "ETH_adm0")  #subset data/remove columns eth <- eth@data[, -(5:67)]   This does indeed leave me only with the first 4 columns, but it also makes the object a regular data frame rather than a spatial data frame ready for mapping. So how do I remove these unwanted columns while maintaining status of SPDF?

My spatial polygon data frame (SPDF) contains too many columns (variables) and I want to remove most of the columns entirely.   I know how to do this with a regular data frame in R, but I am unsure how to do this when dealing with object of class SpatialPolygonsDataFrame?


I am familiar with c but new to c++.  What is the difference between below two functions? How the both the programs functionally same? How actually the address is passed in scenario 1 and values are modified without de-referencing the variables.  Scenario 1      void duplicate (int& a, int& b, int& c)     {     a*=2;      b*=2;     c*=2;     }      int main ()     {     int x=1, y=3, z=7;     duplicate (x, y, z);      cout << "x=" << x << ", y=" << y << ", z=" << z;     return 0;     }   Scenario 2      #include <iostream>     using namespace std;      void duplicate (int *a, int *b, int *c)      {     *a*=2;     *b*=2;     *c*=2;     }      int main ()     {     int x=1, y=3, z=7;     duplicate (&x, &y, &z);     cout << "x=" << x << ", y=" << y << ", z=" << z << endl;     return 0;     }

I know references are syntactic sugar, so code is easier to read and write. But what is the difference between a pointer variable and a reference variable?


On diagrams the transistor have usually a direction - it is assumed that (for bipolar NPN) current goes from base to emitter and it is reflected in symbol:         – Schematic created using   However when if I look how transistors are actually being built it seems that there is no difference between collector and emitter - both are N regions (for NPN transistors). Is there a difference between them I can't see or is it just a convention to allow reader get the intended direction or current?  (I described bipolar but I'm also interested in FETs)

the (surely simplistic) model of a bipolar junction transistor one is taught in foundational physics course appears to be symmetric. - So, what is the difference between the collector and the emitter of a real BJT? If the transistor were symmetric one would not make this distinction...  Also:   Do BJTs have a 0.6V voltage drop like diodes? Are BJTs conductive in both directions, i.e. E-C and C-E?   Many thanks.


– Schematic created using  I have a constant current load circuit using a sense resistor and discrete quad op-amp set up as a 3 op-amp instrumentation amplifier and using the 4th to drive the gate of a MOSFET. The circuit oscillated for a long time until I dropped the gate driving op-amp feedback resistors to fairly low values and then  it worked fine for a while. I did some load testing of the MOSFET itself (controlling the gate with a POT) to see how well it could handle heat and if the heatsink would do any good. It got crazy hot (starting melting it's own solder) but it still works and isn't shorted. I could try replacing the MOSFET with a new and less abused one but I'd like to have this circuit be less vulnerable to oscillating in general so if I can get it working with this one I'd prefer.

I've been trying to make a current source, and have finally gotten my hands on some  which should be an 'unlimited cap drive' op-amp. The problem is, it is still oscillating. This is the schematic and PCB layout:   I have tried to route the ground inside the loop area, close to the 5V connection for the opamp, so I could place the bypass capacitors as close as possible. Although the bigger 10uF cap has one of its legs at the groundplane (forgot to include this cap in the schematic picture.) This is what it looks like when I probe the gate of the MOSFET:  It's all over the place. I tried adding a 10uF capacitor across the DUT, so from VDD to ground. This removed a lot of the wierd noise and made it look almost like a sinewave:  I've tried with and without the gate resistor R1, it didn't seem to make any difference. What is going on? Any clues on why this just doesn't work? EDIT: Solved it! With the help from @Andyaka below, I used his solution of inserting a BJT emitter follower in between the op-amp and the MOSFET, together with an integrator and got some great results! Final circuit:  The simulations can be seen here:  The gain/phase bode plots I made on the PCB:  Bandwidth of approximately 350kHz! Very pleased.


In an algebraic system, an element  that behaves like $0$ does for addition or like 1 does for multiplication of real numbers is called an " identity element" ;  an element that is to some element $a$ like $\frac 12$ is  to 2 is called an inverse element of $a$.   Is there a general name for an element that behaves like $0$ does for multiplication?   I mean, a general  name  for an element $n$ having this property :  $ \forall(a) a * n = n*a=n$ , $*$ being a binary operation?

Is there a general name for the following properties, (similar to the properties of existence of an additive identity, existence of multiplicative identity etc):   For any given set, the intersection with the empty set results in the empty set. For any real number, multiplication with zero results in zero.