So I borrow this camera from my mom who likes photography, but doesnt use it anymore. Its a Canon 350d.  I've just started photography and quickly realise that i cannot crop that much without sacraficing much image quality.   The lenses I have is:  Kit lens 18-55mm Zoom lens 80-200mm ()  I'm planning on eiter buying a new body. Or use the money to buy a new lens, like a 50mm prime or a 300mm zoom lens. I also dont think my camera can whitstand weather that much. This is bad since I live in the arctic region with snow most of the year. So what do you think?

As the question says, when should I upgrade my camera body? In particular, if I have a low- to mid-range body (A DSLR such as a Nikon D3200 or Nikon D5100, or Canon SL1 or T5, or a mirrorless camera such as a Panasonic GH3 or an Olympus E-PL6). How do I know when I need to upgrade?  I have a complement of "kit" lenses, such as an 18-55mm f3.5-5.6 and a 55-200mm f4-5.6. Maybe I've even added a 50mm 1.8 to the kit. Flash is only for indoors (right?) and I usually shoot outside, so that means I don't need an external flash.  I shoot photos of my family and friends whether out at the park or having a picnic, my kids sports practices and games, vacation photos, as well as some landscapes, flowers, and whatever else catches my eye. Pretty familiar territory. I'm not a professional and don't intend to become one.


Please tell me how to solve this one. Given that $m, n$ are positive real numbers and $m>n>0$. Prove that $(1+\frac1m)^m > (1+\frac1n)^n$.   Now I am willing to prove this through elementary inequality techniques( like AM-GM inequality etc). I know that the same can be proved using calculus and the fact $\{(1+\frac1x)^x: x >0\}$ is an increasing function.   But without using the calculus stuff, can we prove it in simple inequality way ?  Thanks in advance

How could we prove that this inequality holds      $$ \left(1+\frac{1}{n+1}\right)^{n+1} \gt \left(1+\frac{1}{n} \right)^{n} $$   where $n \in \mathbb{N}$, I think we could use the AM-GM inequality for this but not getting how?


How do I to add a chapter-name to this dedication and to add it to TOC, please?  \newenvironment{dedication}   {\clearpage           % we want a new page    \thispagestyle{empty}% no header and footer    \vspace*{\stretch{1}}% some space at the top     \slshape             % the text is in italics    \raggedleft          % flush to the right margin   }   {\par % end the paragraph    \vspace{\stretch{3}} % space at bottom is three times that at the top    \clearpage           % finish off the page   } %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{dedication} ABC \\ DEF \end{dedication}   I'm using report class. Thanks a lot!

How do I include a chapter reference within the table of contents without giving it a chapter number? I am using the report document class.  Normally, I would create a chapter as follows:  \chapter{Some Chapter}   but this results in the chapter being given a number. Currently I am using  \chapter*{Some Chapter}   which gets rid of the number, but then it is absent from the table of contents.


I am trying to figure out how to summon a custom villager with multiple custom trades. Can you help me make a command? I am trying to trade 4 emeralds for a pair of diamond boots with protection 1, 8 emeralds for a pair of diamond boots with protection, too.

I'm trying to set up a shop system in a vanilla minecraft realm and villagers seem like the most streamlined method of doing so, however I'd also like to make it so that other players on the server can program their own villager, or have me program it for them as an operator so that other players can trade with each other through the villager. I figure that since villagers now have a secret inventory, they can collect items, but I was wondering if there's any way to access the items traded to them or if they just disappear.  Currently my thoughts are that a player would initiate a trade, the villagers sells would be linked to individual slots in a chest and the villager buys could be linked to another chest, allowing the player to fill a chest and thus 'program' their villager, and that finally a third chest would be filled with the item the villager receives, while the chest containing the trades would decrement the specific number of the item in the relevant slot.


This is not a duplicate of the questions posted   and   It is a duplicate of the question posted  however there is no answer to that question and one of the commenters is wrong about the direction of sharing. I am posting this again to hopefully get a solution for this.  I have enabled internet sharing in OSX via settings -> sharing then clicking on internet sharing. I have tried this using wifi which works just fine, however I am no longer allowed to create a wifi network because security.   My new plan is to use the iPhone USB option to share my Mac's ethernet connection with my iPhone. The setup seems simple and I have selected "Share your connection from: Ethernet" "To computers using: iPhone USB". I don't currently have a connection to the internet. Is there something else I need to do?

I have an iMac, connected to the Internet via Ethernet, and an iPhone 4. I would like to share the iMac's Internet connection to my iPhone via the USB Cable (because my wife dreams of a wifi-less household).  I've set up Internet Sharing, specifying "sharing from: Ethernet  via: USB IPhone", but when I test, the iPhone cannot connect to the Internet. Is there something I need to activate on the iPhone?   iMac, mac os x version: Mountain Lion, 10.8.4 iPhone 4, IOS Version: 6.1


I just installed 14.04 over my old 12.04 partition on my Macbook Pro 10,1 (which is dual-booting with OS X) by following the instructions . The only difference is that I'm using rEFInd instead of rEFIt. The proprietary NVIDIA drivers worked great with 12.04, but now I'm unable to boot into Unity with it in 14.04.  Generally, I just get a black screen after the Grub menu, though occasionally I get some kind of panic screen like , where I see errors like:   [drm: __gen6_gt_force_wake_mt_get] *ERROR* Timed out waiting for forcewake old ack to clear. [drm: __gen6_gt_wait_for_thread_c0] *ERROR* GT thread status wait timed out [drm: __intel_ring_setup_status_page] *ERROR* render ring: wait for SyncFlush to complete for TLB invalidation timed out   etc.  Using the nouveau drivers works fine, but everything feels sluggish so I would really like to get the NVIDIA drivers working.  Has anyone successfully gotten the NVIDIA drivers working with the GT-650M Mac Edition?

I recently made the switch to Ubuntu. Everything on my laptop works fine except my hybrid graphics card. It is Intel graphics combined with Nvidia GeForce GT650M. I tried Bumblebee, but primusrun doesn't work (segmentation fault, core dumped) and optirun works with glxspheres64, but steam games look worse with optirun than with Intel graphics (e.g. Surgeon Simulator 2013 runs fine with Intel and hangs a lot with optirun)   I tried Nvidia Prime, but it gives me a black screen on startup after install, so I can't do anything and have to power off my PC with the power button. I also tried nvidia-prime 0.5 on Ubuntu 14.04, and then I get 'low-graphics mode' and I can't get to Unity.


If a number N is given to us. Is there any way to find all the combinations of numbers whose LCM is N?

How can we show that the number of pairs $(a,b)$ (where the pairs $(a, b)$ and $(b, a)$ are considered same) with $\operatorname{lcm}(a, b) = n$ is equal to $$\displaystyle\frac{(2e_1+1)(2e_2+1)...(2e_k+1)+1}{2},$$ Where $n=p_1^{e_1}p_2^{e_2}\dots p_k^{e_k}$, $p_i$s are prime for all  $1\leq i\leq k$. I managed to guess this formula for a programming problem I was working on, but I'd be interested in a deduction or proof.


I am frequently having to adjust my brakes because of brake pad wear. I do not have to do major braking. Are there other brake pads that wear longer that do not cost big bucks? Thanks, Andy

Looking around for rim brake pads, I have noticed a wide variety:   low end-ish: cheap, rubber pad with metal stem, unknown brand high end-ish: expensive, rubber pad with metal stem, known brand cool end-ish: dedicate pad sections (1 for dry, 1 for mud, 1 for rain)   Is there any good reason to go for an high end-ish or for the cool end-ish, or is it just plain old marketing tricks?


As defined (for example, in Wikipedia):  Completeness is a property of a statistic in relation to a model for a set of observed data. In essence, it is a condition which ensures that the parameters of the probability distribution representing the model can all be estimated on the basis of the statistic: it ensures that the distributions corresponding to different values of the parameters are distinct.  A sufficient statistic is minimal sufficient if it can be represented as a function of any other sufficient statistic. Intuitively, a minimal sufficient statistic most efficiently captures all possible information about the parameter θ.  What I am looking for is a way to visualize either of these two explanations (intuitions?) in some way.  Any suggestions on how that might be done?

As stated by Wikipedia:     A sufficient statistic is minimal sufficient if it can be represented as a function of any other sufficient statistic. In other words, $S(X)$ is minimal sufficient if and only if   $S(X)$ is sufficient, and   if $T(X)$ is sufficient, then there exists a function f such that $S(X) = f(T(X))$.   Intuitively, a minimal sufficient statistic most efficiently captures all possible information about the parameter $\theta$.   I have some trouble understanding the full meaning of "minimal"  What I don't get is, what happens if we have a third sufficient statistic, that we call $U(X)$ such that:  $U(X)=g(S(X))=f(g(T(X)))$  In this case are both $U(X)$ and $S(X)$ minimal? I ask this because minimal makes me think that it must be the "most minimal" so there can be only one (group) of minimal statistics.  If I am not wrong if f or g are invertible Then the three sufficient statistics are all minimal but in this case they all belong to the same group. In the case f and g are not invertible,the three statistics: $U(X),S(X),T(X)$ have all different efficiency in capturing information


I tried catching like 20+ Pokemon, but when I throw the Pokeball, it ticks 1 time, and they run, even though they are CP 10.  I'm currently level 17. What's wrong?

I can't do anything now. Can't catch Pokemon, can't get items. Does anyone have the same problem?


I am new to photography and I am planning to buy a Nikon D3300 (with 18–55 mm kit lens) to start with, after reading through the reviews. But one question lingering on to my mind even after reading multiple posts here is whether there is any option to buy any other lens type, of any other brand — say Canon or Sony — to fit in to this camera.

I've got some lenses of brand X, but I've just got a new camera of brand Y. How can I tell if it's possible to use my lenses on my camera? I accept that I may lose a lot of automatic functionality like autofocus, aperture control and metering when using an adapter to connect the two.


I wonder if the belief that there is no truly stationary frame of reference is really true.  Here's my thinking, please poke holes in it and/or mock me :)  As we understand it, before the big bang the whole universe was a tiny dot, a singularity. At some cue or input or serendipity, that dot began expanding. When that singularity expanded to the size of a beach ball, or perhaps the earth, it should have had a center spot. Let's call that spot the Universe's Core. Couldn't we call that spot the One True Universal Frame of Reference? If not, why not?

TV documentaries invariably show the Big Bang as an exploding ball of fire expanding outwards. Did the Big Bang really explode outwards from a point like this? If not, what did happen?


First Question for me.  I have benefited from other answers here but have not fully resolved my problem.  Here's my problem...  The LM311 Comparator output does not drive the N channel MOSFET fully on.  The LM311 has a 110mv ref voltage on the inverting input. The non-inverting input is driven by an opto-isolator output. The Opto-isolator is driven by 1 of 4, AC 60Hz voltages.  <1VAC, 9VAC, 55VAC and 115VAC.  The goal of the design is to have the FET fully turn on the 12VDC fan when there is appreciable AC voltage.  So fan fully On for the 9, 55, and 115VAC voltages.  It seems it should work because I measure voltages on the non inverting input of 1.6, 2.2 and 3VDC respectively for the 3 appreciable AC voltages.  And my ref voltage on the inverting input is 110mv.  So it "almost" works because the fan is off at the <1VAC, but not fully "On" for the other AC voltages.  I believe this is because Vgs is 167mv, 6.1V, 7.7V and 9.9 Volts for the 4 AC voltages listed above.  And the fan is only getting 7, 8 and 10VDC instead of a desired 12VDC. Would really like to be able to fully turn this FET all the way on.  So Close!  Any input or guidance is appreciated.  Ps-Things I think I've done right? Flyback diode across the fan. Putting N channel FET to switch to ground on low side of fan. LM311 has Open collector output using correctly?  PSS-I realize that the pinouts for the LM311 are not right in my schematic.  I have them right in my protoboard circuit.  Its a single device.  Pin 2 is noninveritng and pin 3 in Inverting  Thanks Again.      The suggested duplicate question and answer doesn't help for the following reasons: Both diagram and schematic are"No file found" making it pretty difficult to follow the answers. I am not using any positive feedback in my circuit as I don't think I need one. I have a simple pull up resistor to my 12V supply, not a voltage divider to the power supply as is mentioned in the answer. Thanks.  Just for the record I wanted to post a more accurate schematic and thanks for the response on using a Cap to hold up the opto isolator output. I actually have a full wave input to the phototransistor but I'm sure the cap will help anyway. To answer the last question, the Pin 7 comparator output has a pullup resistor to 12v. The issue is still that Vgs is only 10v when the comparator has 3v on pin 2 and 110mv on pin 3. I would have expected the LM311 output to go much closer to 12v (Vcc) with those inputs. The intent is for the FET to go completely on for pin 2 voltage > pin 3.

I have the following circuit, where I put R52 = R53 = 2700 Ohms :    Triggering levels are of 1V and 2V approximately according to my computations, that is okay according to the following figure showing input in green and output in blue :    But what I find really strange is that the maximum voltage output is around 3.3V and not at 5V. How would you explain that ? And last detail : how would you explain that the output is not exactly at 0V when the input is high?  Thank you very much for your help.


I am using Koma-script for a report.  \documentclass[titlepage,12pt,a4paper,toc=bibnumbered,numbers=endperiod]{scrreprt}   I would like to give multiple option to "toc" option such as bibnumbered, flat, chapterentrywithdots etc. instead of just one.   How can I do this?   I am a newbie so please bare with me...

Title says it all, but here's an example: the KOMA-Script classes provide the option toc which can have multiple values that don't interfere with each other, like values that enable the Bibliography in the TOC and others that just influence the layout of the TOC. When I need several of these values for the class option toc, how can I pass them all together to toc without having to repeat toc= all the time?  What I have currently:  \documentclass[toc=listof, toc=bibliography, toc=flat]{scrbook}   Idea of what I'd like to have (but what does not work)  \documentclass[toc={listof, bibliography, flat}]{scrbook}   Is this somehow possible? If yes, how?


I always wanted to play D&D but i was always "friendless" amd live in a very urban area where no one plays i learn better if others teach me are there any videos that anyone could suggest that is helpful or any groups that are willing to take beginners?

I have been told that roleplaying is great fun. I've looked and looked and it all seems so complicated. Could anyone tell me a good place to start, and what sort of things you end up doing in roleplaying?


An old logic question goes something like this:     A teacher tells her students on Monday that there will be a test this week, but they will not know on which day till the morning of. The students think about this and come to the conclusion that there will be no test this week. Why?   The accepted answer to this is that the test cannot be on Friday, since that's the last day it could be on, so the students would know the night before it had to be that day. Therefore the test must occur by Thursday. However the test cannot occur on Thursday, since that's the last day it could occur on, so they would know the night before. They apply this logic recursively, eliminating every day this week, and decide therefore the test cannot occur this week.  Suppose the teacher then had the test on Thursday (or Wednesday, or whathaveyou). None of the students would see it coming, so clearly their logic fails at some point.  What is the exact error in their logic?

I just remembered about a problem/paradox I read years ago in the fun section of the newspaper, which has had me wondering often times. The problem is as follows:  A maths teacher says to the class that during the year he'll give a surprise exam, so the students need be prepared the entire year. One student starts thinking though:   The teacher can't wait until the last day of school, because then the exam won't be unexpected. So it can't be the last day. Since we've removed the last day from the list of possible days, the same logic applies to the day before the last day. By applying 1) and 2) we remove all the days from the list of possible days. So, it turns out that the teacher can't give a surprise exam at all.   Following this logic, our student doesn't prepare for this test and is promptly flunked when the teacher does give it somewhere during the middle of the year (but that's my own creative addition to the problem).  This problem reminds me about the  for finite number of turns - you have to betray at the last turn because tit-for-tat retaliation is no longer relevant (no next turn), but then that means that you have to betray at the turn before that, and so on, until you reach the conclusion that you can't cooperate at all.  So is the student's reasoning correct or not? Mathematically it looks like it should be, but that would imply that surprise exams are not possible (and they are).


Is there a formula to calculate how long it will take for a nichrome (NiCr-A) rod of given dimensions to heat up to a certain temperature (or maximum temperature) for a given supply of AC or DC current and voltage to the rod. Assume the rod is surrounded by stationary air at ambient temperature (~25°C).

Let's say I have 1m of 2,5mm² copper wire, insulated with H07V-K. The wire carries 40A and environment temperature is 25°C. The wire is suspended in free air. How hot will the wire get? And how can I calculate it for other values?  The use case is a 12V-230V AC converter I want to hook up to my car and determine the minimum wire thickness required. Because it's only used from time to time and not buried in a wall I suspect I can use thinner wires. This is a temporary thing and doesn't need to be up to code.


I am trying to cron an rsync sync over ssh, but for some reason, as soon as I put the command in cron, it won't run. I don't know what is causing it to break, but it is certainly something related to the fact that it is placed in cron because:   If i copy paste the command in my shell prompt, it will execute as expected. if I replace the command in cron by a simple command such as date > /root/synclog.log, cron does fire it up as expected.   Here's the code:  * * * * * flock -n /root/synclockfile -c "rsync -avv --stats -h --log-file=/root/synclog.log --log-format='%t %f %b' --ignore-existing -e ssh /shares/myshare/PHOTOS/ my_server_hostname:/backups/PTHOTOS"   What could be wrong?

I want to create a log file for a cron script that has the current hour in the log file name. This is the command I tried to use:  0 * * * * echo hello >> ~/cron-logs/hourly/test`date "+%d"`.log   Unfortunately I get this message when that runs:  /bin/sh: -c: line 0: unexpected EOF while looking for matching ``' /bin/sh: -c: line 1: syntax error: unexpected end of file   I have tried escaping the date part in various ways, but without much luck. Is it possible to make this happen in-line in a crontab file or do I need to create a shell script to do this?


I have a very strange problem. When I press stop, the code does not stop. see: import tkinter as tk x=tk.Tk() stops=False def stop():     stops=True     print("STOPPED") tk.Button(x,command=stop,text="Stop").pack() while not stops:     print(stops)     x.update()     x.update_idletasks()  If I press stop, why does still it keep on printing? the stops variable is not edited in the while loop, so why doesn't it stop? I have also tried adding this to the end of the while loop: if stops:     break  But it still does not stop. Why?

What exactly are the Python scoping rules?  If I have some code:  code1 class Foo:    code2    def spam.....       code3       for code4..:        code5        x()   Where is x found?  Some possible choices include the list below:   In the enclosing source file In the class namespace In the function definition In the for loop index variable Inside the for loop   Also there is the context during execution, when the function spam is passed somewhere else. And maybe  pass a bit differently?  There must be a simple reference or algorithm somewhere.  It's a confusing world for intermediate Python programmers.


For a bash script I'm making, I need to delete all but the newest 2 files in a directory.  I decided to use ls -tUr > somefile.txt and then just tail the newest 2, move them somewhere else, rm *, and move them back.  For some reason, somefile.txt actually shows up (among the rest of the files) inside somefile.txt which screws up using the tail command.  So my question is, logically ls would return the current folder/files and then be redirected into somefile.txt, but clearly this isn't happening since somefile.txt must exist before ls runs; why is this?

I often see tutorials online that connect various commands with different symbols. For example:  command1 |  command2 command1 &  command2 command1 || command2     command1 && command2   Others seem to be connecting commands to files:  command1  > file1 command1  >> file1   What are these things? What are they called? What do they do? Are there more of them?    .


I occasionally want to use my Ubuntu machine as a desktop but mostly  as a headless file server.  Before I upgraded to Oneiric, I  used rcconf services to disable or enable the desktop.  In Oneiric I  don't see GDM; so can't uncheck it.  LightDM appears but isn't checked. I don't see anything else that looks like a desktop.  So, how can I disable, an occasionally enable, the Oneiric desktop?

Is it possible to disable X at boot time? I'm setting up a server so it would be nice if it wouldn't load the graphical interface every time I boot.


I have a table like this in ConTeXt, per a workplace template, with borders around every cell.  \startsetups table:all     \setupTABLE[align={hyphenated, normal}]     \setupTABLE[frame=on] \stopsetups \startsetups table:three     \setupTABLE[column][1][width=0.333\textwidth, align=right, distance=0.05\textwidth]     \setupTABLE[column][2][width=0.333\textwidth, align=right]     \setupTABLE[column][2][width=0.333\textwidth, align=right] \stopsetups  \starttext     \startTABLE[setups={table:all, table:three}]         \NC column 1 \NC column 2 \NC \input knuth \input knuth \input knuth \input knuth \input knuth \input knuth \input knuth \input knuth  \NC\NR     \stopTABLE \stoptext   The data in each column is very long, so unfortunately, the data disappears off the bottom of the page.  I tried split=yes, but that splits the table, not the middle of cells. Huge cells still run off the bottom of the page.  How can I get the table cells to be split in half so that the data continues onto the next page?

I've got a following fragment to display in two columns:  Some heading    Some longer                 description                   * with                   * a                   * list   I'm using the following def:  \def\DataPair#1#2{%    \defineparagraphs[TwoColumns][n=2]%    \setupparagraphs[TwoColumns][1][width=\LeftColumnWidth,align=left]%    \startTwoColumns%       {\tfx{\sc #1}}%    \TwoColumns%       {#2}%    \stopTwoColumns% }   Where the content is:  Some longer description \startitemize[packed]    \item with    \item a    \item list \stopitemize   Unfortunately the that block ignores page breaking. Is there some way I can allow \DataPair to page-break at any point?


A file is modified by a script using an input file-     141,141_1,BAR,HONDA,ps2_0,unassigned,ps3_0,Unassigned,ps4_0,Unassigned,ps5_0,Unassigned,ps6_0,Unassigned,ps7_3,TILL WILL,.....   Input file-     141,ps7,TILL WILL   Now I need to search whether to column ps7_3 is updated with the correct value.  So from the input file, I separated the columns-  while read -r line; do sub1=$(echo $line|cut -f 1 -d ','); sub2=$(echo $line|cut -f 2 -d ','); sub3=$(echo $line|cut -f 3 -d ','); sub4=$(echo $sub2'.*,'$sub3|sed -e "s/\(.*\)\r/'\1'/"); echo $sub1; echo $sub2; echo $sub3; echo $sub4; grep $sub4 modded_file.csv.dat; done<input.csv   The output being-  141 ps7 TILL WILL 'ps7.*,TILL WILL' grep: WILL': No such file or directory   But when I run     grep 'ps7.*,TILL WILL' modded_file.csv.dat, it works. How can I grep a variable as shown above, in a file?

If you've been following unix.stackexchange.com for a while, you should hopefully know by now that leaving a variable unquoted in list context (as in echo $var) in Bourne/POSIX shells (zsh being the exception) has a very special meaning and shouldn't be done unless you have a very good reason to.  It's discussed at length in a number of Q&A here (Examples: , , , )  That has been the case since the initial release of the Bourne shell in the late 70s and hasn't been changed by the Korn shell (one of ) or bash which mostly copied the Korn shell, and that's how that has been specified by POSIX/Unix.  Now, we're still seeing a number of answers here and even occasionally publicly released shell code where variables are not quoted. You'd have thought people would have learnt by now.  In my experience, there are mainly 3 types of people who omit to quote their variables:   beginners. Those can be excused as admittedly it's a completely unintuitive syntax. And it's our role on this site to educate them. forgetful people. people who are not convinced even after repeated hammering, who think that surely the Bourne shell author did not intend us to quote all our variables.   Maybe we can convince them if we expose the risk associated with this kind of behaviours.  What's the worst thing than can possibly happen if you forget to quote your variables. Is it really that bad?  What kind of vulnerability are we talking of here?  In what contexts can it be a problem?


Sometimes it happens that I make some changes in my working directory, and I realize that these changes should be committed in a branch different to the current one. This usually happens when I want to try out new things or do some testing and I forget to create a new branch beforehand, but I don't want to commit dirty code to the master branch.  So, how can I make that uncommitted changes (or changes stored in the index) be committed to a different branch than the current one?

How can I do the following in Git?  My current branch is branch1 and I have made some local changes. However, I now realize that I actually meant to be applying these changes to branch2. Is there a way to apply/merge these changes so that they become local changes on branch2 without committing them on branch1?


Let $H$ generated by some generators $H=\langle h_1, \ldots, h_n\rangle$ $(n\gt 1)$. My question is whether there exists any monoid $H$ such that $H$, is infinite and $H$ is not a free monoid and $H$ does not contain any free monoid?

Let $H= \langle h_1, \ldots , h_n \rangle$ ($n>1$) be an infinite monoid that is not a free monoid. Does $H$ contain an isomorphic copy of a free monoid as a submonoid? EDIT. It is a natural question. The corresponding question for groups is the Burnside problem.


I need to find a subgroup of $S_4$ that has order 12 other than the subgroup of even permutations or anything isomorphic to it. What is the procedure to go about finding such a subgroup?

The subgroup in $S_4$ that I know has order 12 is the subgroup of all even permutations, otherwise known as the alternating group $A_4$. However, I know this from a fact and not because I am able to show a subgroup of order 12 exists in $S_4$ in the first place. If I had not been told there existed a subgroup of order 12 in $S_4$, I would not have known there was one. So I guess this is actually a two-parter for me: 1) How do I go about showing that a subgroup of order 12 does indeed exist in $S_4$? I know by Lagrange that if there exists a subgroup, then the order of that subgroup must divide the order of the group. However, this doesn't say anything about the existence of the subgroup. And Sylow only verifies subgroups of a prime to some power order, which 12 is not. I also know that there might be a cyclic subgroup of order 12, but without manually multiplying every possible permutation in $S_4$, I don't know any other way to check the existence of this or if this subgroup is isomorphic to $A_4$ because I don't know how to write these permutations as functions in order to check if there is a homomorphism (I know that a permutation is bijective by definition). And 2) How do I show that this group of order 12 is the only group of order 12 in $S_4$?


I found that some straightforward code results in an unexpected (and incorrect) inequality comparison on GCC 4.6.1 vs Visual Studio (2008 & 2012) or Clang 7.3.0 on OSX.  Here's a reduced snippet:  typedef float ftype; struct Foo {     ftype v;      Foo(): v(16.0f / 60.0f) {}     ftype val() const {return v * 60.0f;} };  void bar() {     Foo f;     ftype v = f.val();     if (v != f.val())         printf("inequal"); }   If ftype is typedef'd as double then the problem doesn't occur. Could this be something to do with compiler inlining? Perhaps actually returning a double instead of a float?

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


Okay, so it's a very hypothetical question.     I'll tell you where I come from ...    Last year, on Stack Overflow there was some sort of fake account made   and I have no idea why that guy/girl upvoted all my answers .My   reputation increased by 200 (That's the maximum ~thank god !) and I   was pretty delighted but the next day I got a huge moderator's notice   and my account was suspended for like 3 months or so [I don't exactly   remember the time :-( ] My reputation became 0 and I could answer no   questions .   My question is:  If I upvote someone's answers genuinely out of interest, will his and my account get turned down the same way?  Finally, I want to know the logic behind identifying scams vs genuine questions.  And also the answer to my above question.

A high-reputation, highly-active user has already been dinged once for a sockpuppet, and I just dinged him again. He probably has another sockpuppet as well.   What are the guidelines for handling users who game the system in this fashion? Specifically,   How can I be sure I'm looking at a sockpuppet? When should sockpuppets be considered a problem? How should moderators handle problematic sockpuppets once they've been identified? I was suspended for sockpuppetting and feel this is unfair


I want to record the contents of a long webpage (even if it's out of my screen). Is there any tool to achieve that?  If video recording is not posible, take screenshot would be sufficient.  Any different approach is also welcome, i.e., if I just thought of a wrong solution and it's possible to enlarge windows without limits and then take a video or a screenshot of it, etc. then don't be afraid to tell.  For instance, if my display is 1280x800 for instance from superuser.com I would like to take a video that is 1280x4800 aprox. so that all the content is grabbed.  Any suggestion?  I'm using Mac OS X Mountain Lion, but any solution to another system would also be upvoted.

On the Mac, how can I take a screen shot of a window that includes the parts that are off-screen and need scrolling to become visible?  The built-in Grab application can capture individual windows, but it only includes the parts that are on-screen at the moment.  Clarification: By "off-screen" I mean parts that are in the window, but are not visible, because the window has scrollbars. I do not mean parts of the window that are simply off-screen because of how the window is positioned (of course, I want those, too).


Can someone give me an example of a simple ring that is not semi-simple ?

I was said that can exists simple algebras $A$ that are not semi-simples in the following sense:   $A$ is simple, i.e. doesn't have non trivial ideals; $A$ is not semi-simple, i.e. is not a semi-simple module over itself.   Does anybody has an example? Thanks in advance


Given a file path (e.g. /src/com/mot), how can I check whether mot exists, and create it if it doesn't using Linux or shell scripting??

What command can be used to check if a directory exists or not, within a Bash shell script?


I used a tab layout with fragment. The scenario goes like this.  Activity:  Fragment 1 , Fragment2 , Fragment3  From Fragment2 Updating the UI of Fragment1.  I tried to access the methods from fragment but resulting null pointer exception.

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?


Yesterday I  and after 2 hours I found a "solution", I would answer, for the first time, at my question and Stack Overflow block my answer with this message:     Oops! Your answer couldn't be submitted because:           Users with less than 100 reputation can't answer their own question for 8 hours after asking. You may self-answer in 5 hours. Until then please use comments, or edit your question instead.)      and I would want to understand why there is this block?  Yesterday I worked around it by adding on my question a block [answer]answer[/answer] as shown at screen shot below and today I modified again the post moving the block out into an answer but, for me, it is strange to have self-answer block.  EDIT: because Cody and Rory ask why I add the tag [ANSWER] on my question the answer is simple: I didn't know how tell that I resolved the problem so I create that tag for underline that it was out of my question and temporarly there...

If we're implementing , why don't we also require that users have at least 1.5 times the amount of reputation needed to ask their current question in order to answer their current question?  I believe this would really reduce the amount of non-answers that should have been edits to the original question, or perhaps a comment under another answer.  Edit  Inspired by marcog's excellent suggestion , perhaps it would make more sense to set a minimum amount of time that must pass before you can answer your own question. New users would need to wait in the neighborhood of six hours, while users with more reputation could answer their own question within minutes if they discovered the solution on their own.  This would get in the way of the behavior that we don't want, which is people posting answers that should have been edits while not annoying most.


As far as I can tell,  simply fixes a dead link, yet it was rejected by two users as "not making post easier to read...".  Is fixing dead links not something we should be doing via edit?

None of the reasons given make sense given the edit:     This edit is incorrect or an attempt to reply to or comment on the existing post.   The post contained a dead link, and I updated the link to the correct current page for the resource.   I stated as much in my edit summary.


I was trying to create some bubbles. Everything was OK in render preview, but render result becomes completely transparent image.   Here you can see render preview. I use HDRi lighting and film transperant.  First sample in render process shows a bit of "envelope" of each bulb.   Here you can see render at 2-3 samples and it's almost invisible.   here is a gif when render runs...   Here is my node setup. I can upload my .blend file if you help me how to do this:) Yes, bubbles are visible, but it brings black background and some bugs.   And the most interesting thing i found when i tried to save this image with black background without alpha.  THIS is the saved rendered image from previous screen!  Here is the comparison between rendered image and render preview at 1 sample.  And at 2 samples.

Bit of an issue here, trying to render this glass scene    Looks fine in the viewport, but when I hit render    Does anyone know the cause of different view port and final render, and how to fix it?  Here's my


Hello Guys I would like to know if it is possible to hide the div if the internet is not availaible. Here is the code    if(navigator.onLine) {       //show } else{ //Hide }      Thanks in advance.

How to detect the Internet connection is offline in JavaScript?


How can I disable all user-installed services on boot by default?  Here is a scenario. I installed ssh server, and by default it is enabled on boot. I know it can be disabled on boot with systemclt command. But how can I default disable any such service(s) on boot? If I install postgresql, mariadb, or any other service, all are set to be enabled on boot by default. I want any of such services to be disabled on boot by default. So I can enable them on boot whenever required.  How can I achieve this? (Fedora, Arch by default have user-installed services disabled on boot by default)  For Ubuntu 16.04

Sometimes installing some applications will start a process or service from the application being run automatically on installation. How do I install without starting them?


For example, if I have an Airport point and I want to create a 30-minute Drive Times buffer polygon around it, how would I do that?  I'm currently using QGIS 3.4.4.

I'm new to QGIS and have tried to create isochrones around points for quite some time. Is there any option to create isochrones on the GUI in QGIS?    I know how to create them using pgAdmin (using eg underdark's explenation and example ()), but I would like to be able to create them using only QGIS.    There is one layer which contains the geocoded addresses around which I need to create the isochrones. It would be great to be able to create different sized isochrones  I've tried to find a plugin or any other option to do this, but nothing seems to work.  I'm using QGIS 2.4.0 on Ubuntu.


I want to prove the famous formula: $\displaystyle\int^{\infty}_0 \frac{\sin{x}}{x} dx = \frac{\pi}{2}.$ There are many ways to do it, for example, by some Fourier analysis. But how about a simple method: integrating just $e^{-xy}\sin{x}$ by $y$ and $x$ successively? Since $|\frac{\sin{x}}{x}|$ is not in $L^1$, Fubini-Tonelli theorem cannot be applicable at first glance. Is this way rigorously justifiable?

A famous exercise which one encounters while doing Complex Analysis (Residue theory) is to prove that the given integral: $$\int\limits_0^\infty \frac{\sin x} x \,\mathrm  dx = \frac \pi 2$$ Well, can anyone prove this without using Residue theory?  I actually thought of using the series representation of $\sin x$: $$\int\limits_0^\infty \frac{\sin x} x \, dx = \lim\limits_{n \to \infty} \int\limits_0^n \frac{1}{t} \left( t - \frac{t^3}{3!} + \frac{t^5}{5!} + \cdots \right) \,\mathrm  dt$$ but I don't see how $\pi$ comes here, since we need the answer to be equal to $\dfrac{\pi}{2}$.


Imagine, there is a big fire in a house and someone is trying to extinguish it by pouring water from a coffee mug. This person has the right intention (the vector of his deeds points in the right direction -- stopping the fire), but insufficient (the vector length is too short compared to a fire -- too little water).  What do you call a situation like this in English?  In other languages there are following idioms I'm aware of:   Drops on a hot stone in German (Tropfen auf dem heissen Stein) Drop in a sea in Russian (Капля в море)    Note that it's different from fixing a hopelessly broken process in that the process the person in question is doing is generally right (pouring water to kill a fire), but its intensity is insufficient.

I'm looking for an idiom to describe something that has a negligible effect.   The only similar question I found here was: , but I'm looking for something else.  I remember it being something to do with water or fire. Something along the lines of throwing a very small amount of water on a large fire? Does anyone know what I'm thinking of?


How do variables work? Is it as simple as using  variable_set('myvar', 'my_value');   to set, and  variable_get('myvar');   to retrieve?  Additionally, where are these variables stored, and do they have any sort of categorisation/access control (i.e. can any module get the variables set by any other module)?  Update from comment  I can see a line like $custom_theme = variable_get('admin_theme', '0'); But i cant see any variable_set('admin_theme') in anywhere in the module though .

I am trying to understand variable_get(). I read so far that you can set variables in the settings.php using the $conf array and retrieve them later in code by using variable_get(). I have read that you can also use variable_get() to retrieve values from the database.   How does this work? Is there a table that is automatically built? How would you set variables if this feature is possible?


Normally one uses visudo to edit /etc/sudoers and perhaps add a line similar to this one kirk ALL=(spock) NOPASSWD: ALL  which will allow the kirk user to become spock. Question I need to create a non-interactive Bash script that will allow user1, user2, user3 to become spock. Does anyone knows how to do that?

I need to edit /etc/sudoers from a script to add/remove stuff from white lists.  Assuming I have a command that would work on a normal file, how could I apply it to /etc/sudoers?  Can I copy and modify it, then have visudo replace the original with the modified copy? By providing my own script in $EDITOR?  Or can I just use the same locks and cp?  The question is more about potential issues than about just finding something that works.


I am having a problem on what I think is a MySQL issue, when I trying fetch a row my the database(mysql) with a column value of ( à¤¹à¤¿à¤‚à¤¦à¥€ í•œêµì–´ Ø§Ù„Ù„ØºØ© Ø§Ù„Ø¹Ø±Ø¨ÙŠØ ), the result row seems exists and truthy on if condition statements. But when I var_dump it, it show empty, not null.  for example: (php/mysql)  Input Data:   id -> 1 name -> Bob address -> हिंदी 한국어 اللغة العربية   Stored Data on Table   [column]id = 1 [column]name = "Bob" [column]address = "à¤¹à¤¿à¤‚à¤¦à¥€ í•œêµì–´ Ø§Ù„Ù„ØºØ© Ø§Ù„Ø¹Ø±Ø¨ÙŠØ"   Expected Data after being fetched from mysql   id -> "1" name -> "Bob" address -> \u00e0\u00a4\u00b9\u00e0\u00a4\u00bf\u00e0\u00a4\u201a\u00e0\u00a4\u00a6\u00e0\u00a5\u20ac \u00ed\u2022\u0153\u00ea\u00b5\u00ad\u00ec\u2013\u00b4 \u00d8\u00a7\u00d9\u201e\u00d9\u201e\u00d8\u00ba\u00d8\u00a9 \u00d8\u00a7\u00d9\u201e\u00d8\u00b9\u00d8\u00b1\u00d8\u00a8\u00d9\u0160\u00d8    $mysql_result_row = array(     "id" => 1,      "name" => "Bob",     "address" => );  echo json_encode($mysql_result_row) // (shows nothing) echo gettype($mysql_result_row) // array echo $mysql_result_row['name'] // Bob echo $mysql_result_row['address'] // (everything stops working, no php nor mysql error logs)     Notes   The sample above have 3 different set of language / character set. à¤¹à¤¿à¤‚à¤¦à¥€ is Hindi í•œêµì–´ is Korean Ø§Ù„Ù„ØºØ© Ø§Ù„Ø¹Ø±Ø¨ÙŠØ is Arabic Don't ask why a single column has 3 different language because I do not know If only one of those languages on that address column, it works, no problem. It only stops working if those 3 combined

I'm setting up a new server and want to support UTF-8 fully in my web application. I have tried this in the past on existing servers and always seem to end up having to fall back to ISO-8859-1.  Where exactly do I need to set the encoding/charsets? I'm aware that I need to configure Apache, MySQL, and PHP to do this — is there some standard checklist I can follow, or perhaps troubleshoot where the mismatches occur?  This is for a new Linux server, running MySQL 5, PHP, 5 and Apache 2.


Is my proof beneath perfect and complete?  I wanted to prove that for any nth root of an integer, if it's not an integer, than it's irrational: $$\begin{cases} m,n\in \mathbb{N}\\\sqrt[n]{m}\notin \mathbb{N} \end{cases}\implies \sqrt[n]{m}\notin \mathbb{Q}.$$  I start by assuming that $m^{\frac 1n}$ is rational and non-integer. So there exist  co-prime integers $a,b$ so that $$\sqrt[n]{m}=\frac{a}{b}$$ $$\implies  m=\frac{a^n}{b^n}\in\mathbb{N}.$$ But since $a$ and $b$ have no common factor, $a^n$ and $b^n$ also have no common factor. So: $$\frac{a^n}{b^n}\notin\mathbb{N},$$ a contradiction.

It is well known that $\sqrt{2}$ is irrational, and by modifying the proof (replacing 'even' with 'divisible by $3$'), one can prove that $\sqrt{3}$ is irrational, as well.  On the other hand, clearly $\sqrt{n^2} = n$ for any positive integer $n$.  It seems that any positive integer has a square root that is either an integer or irrational number.        How do we prove that if $a \in  \mathbb N$, then $\sqrt a$ is an integer or an irrational number?      I also notice that I can modify the proof that $\sqrt{2}$ is irrational to prove that $\sqrt[3]{2}, \sqrt[4]{2}, \cdots$ are all irrational.  This suggests we can extend the previous result to other radicals.        Can we extend 1? That is, can we show that for any $a, b \in \mathbb{N}$, $a^{1/b}$ is either an integer or irrational?


I have a Ubuntu 20.04 server which is reporting relatively low free RAM: top - 11:28:31 up 5 days, 20:12,  3 users,  load average: 0.18, 0.26, 0.27 Tasks: 268 total,   1 running, 267 sleeping,   0 stopped,   0 zombie %Cpu(s):  0.1 us,  0.3 sy,  0.0 ni, 99.5 id,  0.0 wa,  0.0 hi,  0.1 si,  0.0 st MiB Mem :   7786.5 total,    506.1 free,   1329.4 used,   5951.1 buff/cache MiB Swap:   4096.0 total,   3965.5 free,    130.5 used.   6020.5 avail Mem      PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND  373096 root      20   0    8200   3996   3316 R   1.0   0.1   0:01.04 top     872 mysql     20   0 2843736 480140  15652 S   0.7   6.0  87:22.66 mysqld     563 root      rt   0  280136  17940   8200 S   0.3   0.2   1:37.67 multipathd     745 syslog    20   0  224320   4812   3396 S   0.3   0.1   1:28.21 rsyslogd       1 root      20   0  169488  10424   6264 S   0.0   0.1   1:44.98 systemd       2 root      20   0       0      0      0 S   0.0   0.0   0:00.12 kthreadd       3 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 rcu_gp       4 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 rcu_par_gp       6 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 kworker/0:0H-events_highpri       9 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 mm_percpu_wq      10 root      20   0       0      0      0 S   0.0   0.0   0:03.55 ksoftirqd/0  The server has 8GB of physical RAM and only 1.3GB free.  The rest seems to be tied up in the buffer/cache.  However, a list of running processes show that the highest consumer is the mysql daemon which is using only 6% of total RAM. Is there a way to report the true memory consumption and how can I free up the buffer/cache?

Why does my server show              total      used      free   shared buffers    cached     Mem: 12286456  11715372    571084        0   81912   6545228 -/+ buffers/cache:  5088232   7198224    Swap: 24571408     54528  24516880   I have no idea on calculating the memory in linux. I think it says that 5088232 is used where as 7198224 is free, meaning it is actually consuming 5GB of RAM?


I had a question about sirens in another section that went unanswered, so I like to start from basics and go from there.  So if you're sitting at home, and hear a heavy truck go by, the kinds that almost shake your apartment.  That's one kind of noise.  You hear the wail of sirens from an ambulance or firetruck, and that's another.  Then there is someone next to you snoring.  That's a third.  I've heard people use the term "white noise" to cancel out or reduce other noise.  Granted I have used various earplugs but they only reduce certain kinds of noise and not that well either.  But looking at white noise, I realized there is so much about it that I don't know. For instance there is also brown noise and pink noise.  There is a sound's loudness, pitch, timber, direction, frequency, etc.  So I figured I ask my question here and get some constructive suggestions or guidance to help me narrow down my search and give it a sort of direction.  I appreciate all your help.    EDIT for MODS: A per knzhou's suggestion, this is not as relevant to physics as it is to biology of hearing.  I decided to post this in cog sci forum. I can't say it's "solved" because it's not, but just want to let you know you can close this if you prefer.

I saw youtube videos that claimed to do this, although I'm quite certain the videos just excluded sound and lied.  However, I am wondering if the physics of this is actually possible - to create a completely negative sound wave that cancels the sound out to a flat line i.e. complete silence.  p.s. I am not referring to white noise, which prevents the sound from being heard by overriding it with a different sound (white noise). Rather, I am referring to making a sound be completely silent by generating the inverse, opposite, or "negative" sound wave.


Hyndman's great explanation of proper time series CV is at the bottom of the page in the following link:   Leave-One-Out illustration in the following link:   In the 'leave one out' illustration if the dataset in the illustration was time series data and was sorted from past to present from left to right, wouldn't it be identical to Hyndman's explanation on Time Series CV?  If not, how so?


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


Let's say a famous researcher contributed only a bit to a research project by a student, and the student could reasonably choose either to include or not include them as a coauthor. Is it beneficial to the student to include them? It seems that having a big name would increase viewership and perceived legitimacy of the paper, while having more coauthors also seems to diffuse the ownership of the work.

In this  it is claimed that authorship is given away for "free" in some fields (e.g., obtaining the funding). The comments to the answer suggest that this is field dependent. I am looking for documentation from a field that suggests that authorship can be given away for "free". For example, the ICMJE has authorship  that put a pretty high bar on authorship. Is there any documentation that suggests that supervising a student or getting funding is enough to warrant authorship?


I some of the "folders" in my home directory are symbolic links to a larger hard drive mounted on /mnt/data.   I would like it if when I click on (for example) Music in my home directory, Nautilus showed ~/Music. Instead it shows /mnt/data/Music. Not a bug exactly... but it would be nice if going "up" went back to my home directory instead of to the mount point.  Is there a way to change the behaviour of Nautilus in this regard?

I use symbolic links to tidy my home folder. This works well in the terminal, since the links create the illusion of normal folders:    In Nautilus, however, the links behave more like , immediately teleporting me to their target:    This is particularly troubling when¹ I later want to navigate "up" to the parent folder, as it strands me somewhere outside of the tree I've carefully tidied.  How can I make Nautilus show symbolic links as normal folders, like the terminal does?  Details   Nautilus did not dereference symlinks in Ubuntu 12.10:   Maybe this new behavior is just a bug? I'm not sure how to tell. Here's what I know:   It's not on the . I've skimmed the  and didn't see anything related. The Nautilus mailing list archive . I received no response from about 120 idlers when posing the question on the GNOME IRC channel. A change was made in Nautilus 3.6 to .  ¹ This is an example. A workaround for this particular scenario does not constitute an answer to my question. Since people seem to be interested in discussing it, though:   Using the Back button is not a suitable workaround; it does not always take me to the parent folder. You can navigate up by pressing Alt+Up. The desired behavior in this example is for "up" to navigate to the parent folder of the symbolic link. The current behavior is to navigate to the parent folder of the target of the symbolic link.


If the rational number $r$ is also an , show   that $r$ is an integer   So $r$ is a rational number that is a root of a polynomial $p(x)$ over the integers, right? I need to show that $r$ is an integer.  I know that for $p(x) = x^n + a_{n-1}x^{n-1} + \cdots + a_0$  we have that $a_0$ is the product of all roots. I don't think it helps because we could have two roots $a/b$ and $b/a$ and their product is an integer, so the fact that the polynomial is over the integers won't do anything in this case.  Somebody have an idea?

Let $A$ be a UFD, $K$ its field of fractions, and $f$ an element of $A[T]$ a monic polynomial.  I'm trying to prove that if $f$ has a root $\alpha \in K$, then in fact $\alpha \in A$.  I'm trying to exploit the fact of something about irreducibility, will it help? I havent done anything with splitting fields, but this is something i can look for.


Given a problem, how does one know whether to use quantum mechanics or classical mechanics?   Take for example electron scattering from a nucleus. The electrons are given a wavefunction in this case. Why not use the classical approach?

Is there any parameter (in terms of physical quantities such as mass, length, charge...) which can be used to decide when to treat a system quantum mechanically and not classically?


I have now simply 2 SQL Server 2012. I want to configure database mirroring between the 2 servers.  My questions are:   How can it automatically change host of one if the other one was dropped ? Is the performance of mirroring acceptable and is there another way to make one as host and other is backup then if the main server was dropped the other works automatically better than mirroring?

I have two SQL server 2012 instances and I want to configure mirroring between the 2 servers with database.  My questions are:  How can it automatically change host of one if the other one was dropped ?  Is the performance of mirroring is acceptable and is there another way to make one as host and other is backup then if the main server was dropped the other works automatically better than mirroring?


I am getting items from a list using caml query. After that I need to export to excel by csom (c#). I dont want to use pnp .

I want to export SharePoint Online List data programmatically using CSOM code in console application.  Can anyone send me CSOM code for the same.


Why it's always login failed even when entered the correct values  import java.util.Scanner;  public class Main  {     /**      * @param args      */     public static void main(String[] args) {         // TODO Auto-generated method stub       String usrname = "aaa";     String usrpass = "aaa";      Scanner sc = new Scanner(System.in);      System.out.println("Enter your username :");     String usrnameInput = sc.nextLine();      System.out.println("Enter your password :");     String usrpassInput = sc.nextLine();       if (usrname  == usrnameInput & usrpass == usrpassInput) {         System.out.println("Login Successful");     } else {         System.out.println("Lofin failed");     }    }  }

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


I hadn't really given this much though before but when I look at the forward voltage drop of a LED, it gives a graph such       Can I simply set the resistor to a value produce a current and get the corresponding forward voltage drop or is there an associated resistor within the LED for which I need to account?

I'm having a bit of trouble understanding currrent limiting resistors in simple LED circuits. I know that I can determine the optimal resistor like so:  \$\displaystyle R=\frac{V_{s}-V_{f}}{I_{f}}\$  But I'm having a hard time understanding how this one value modifies the voltage and the current to the correct values for the LED. For example, if my calcuations for a super bright blue LED (with \$V_{f}\$ being 3.0-3.4 V and \$I_{f}\$ being 80 mA, and a voltage source of 5 V) gives me 25 ohms (using the lower bound of the forward voltage), that's fine. So the current throughout should be 80 mA and the voltage drop for the resistor and LED should be 2 and 3 volts, respectively.  But what if I used a 100 ohm resistor instead? Or any other value—how would I calculate the voltage drops and current? Would I assume one of them stays the same?


As far as I understand. Serial means data is being sent one by one instead of parallel where multiple bits of data are streamed simultanously. Howewer connections like SATA and USB 3 actually have more than 2 data pins. So in the end what is the real meaning of serial and parallel?

Intuitively, you would think that parallel data transmission should be faster than serial data transmission; in parallel you are transferring many bits at the same time, whereas in serial you are doing one bit at a time.  So what makes SATA interfaces faster than PATA, PCI-e devices faster than PCI, and serial ports faster than parallel?


As I was adjusting my settings I realized that my GPU is not recognized for CUDA at Cycles tab. I tried everything afterward to make it appear- went to Nvidia developers website to download CUDA toolkit(10 version as 11 is not supported on MacOs), reinstall blender, etc.. but it still does not work... Could anyone please help me here? Thanks for your help!

Until now until Blender 2.83.4 my GPU NVIDIA GeForce GTX TITAN X 12288 MB is recognized via CUDA. With Blender 2.90 and Blender 2.90.1 no GPU is seen, also not under CUDA. What is wrong? I'am therefor still working with 2.83.4 My computer Mac Pro (mid 2012) 2 x 3,46 GHz 6-Core Intel Xeon / 96 GB 1333 MHz DDR3 - Mac OS High Sierra 10.13.6


I want to write a JavaScript function reverseArrayInPlace(origin) that reverse an array in place. That is,   let orignalArray = [1, 2, 3];  reverseArrayInPlace(orignalArray);  console.log(orignalArray); // [3, 2, 1]   I know there is a trick that uses the Array.pop() method, by pushing the popped value to an empty result array, then return that result array. But it turns out the original array will become empty.  In order to modify the original array, I've tried it to assign the value of result reversed array to the original array (the argument), then return the original array. Using below three approaches:  origin = result;  origin = [...result];  origin.push(...result);  And here comes my question, the first or second does not work as I expected, but the third works fine.  function reverseArrayInPlace1(origin) {     let result = [];     while (origin.length > 0) {         result.push(origin.pop());     }     origin = result; // not work     return origin; }  function reverseArrayInPlace2(origin) {     let result = [];     while (origin.length > 0) {         result.push(origin.pop());     }     origin = [...result]; // not work     return origin; }  function reverseArrayInPlace3(origin) {     let result = [];     while (origin.length > 0) {         result.push(origin.pop());     }     origin.push(...result); // it works     return origin; }  let orignalArray1 = [1, 2, 3]; let orignalArray2 = [1, 2, 3]; let orignalArray3 = [1, 2, 3];  reverseArrayInPlace1(orignalArray1); // [3, 2, 1] reverseArrayInPlace2(orignalArray2); // [3, 2, 1] reverseArrayInPlace3(orignalArray3); // [3, 2, 1]  console.log(orignalArray1); // [] console.log(orignalArray2); // [] console.log(orignalArray3); // [3, 2, 1]   The return value of above functions is Ok, but the console.log result of the first and second is not what I want.  Can some one explain why the original array's value not changed after function return when I assign the result array to it directly using =? And why it changes as expected when using push()?

The primitive types (number, string, etc.) are passed by value, but objects are unknown, because they can be both passed-by-value (in case we consider that a variable holding an object is in fact a reference to the object) and passed-by-reference (when we consider that the variable to the object holds the object itself).  Although it doesn't really matter at the end, I want to know what is the correct way to present the arguments passing conventions. Is there an excerpt from JavaScript specification, which defines what should be the semantics regarding this?


Show that if $u,v\in H^s(\mathbb{R}^n)$ for $s>{n\over 2}$, then $uv \in H^s(\mathbb{R}^n)$ and $$ \|uv\|_{H^s(\mathbb{R}^n)} \le C\|u\|_{H^s(\mathbb{R}^n)} \|v\|_{H^s(\mathbb{R}^n)}, $$ the constant $C$ depending only on $s$ and $n$.  Progress  I tried to prove by induction on the order of the derivatives, but to use the inductive hypotheses could not get the term right inequality. My problem is to find the appropriate method to be able to solve actual inequality.

How do you prove that the Sobolev space $H^s(\mathbb{R}^n)$ is an algebra if $s>\frac{n}{2}$, i.e. if $u,v$ are in $H^s(\mathbb{R}^n)$, then so is $uv$? Actually I think we should also have $\lVert uv\rVert_s \leq C \lVert u\rVert_s \lVert v\rVert_s$. Recall that $\lVert f\rVert_s=\lVert(1+|\eta|^2)^{s/2}\,\hat{f}(\eta)\rVert$, the norm on $H^s(\mathbb{R}^n)$. This is an exercise from Taylor's book, Partial differential equations I.


This is out of curiosity. I am working with rf 433 MHZ transmitter receiver module. I just wanted to ask whether it affects health in any way. I have read that such radiation has carcinogenitic effects. Does the power transmitted by the transmitter has any effect?

I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use  ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?


I have been editing my .bashrc file to run some commands, such as appending directories to the PATH variable. However, from my knowledge, .bashrc is only executed when a terminal is opened. (Correct...?) In this case, in order to make the necessary changes to PATH, I would need to open up a terminal each time I log on to Ubuntu.  This doesn't seem like a very elegant thing to have to do, particularly for people who tend not to use the terminal much. Is there a way to run these commands when Ubuntu boots up, without requiring a terminal to be opened?

There's a GUI in Windows to edit the path variable. I was wondering if there's something equivalent in Ubuntu to do the same.


I first installed Ubuntu 14.04 from live USB and after confirming that it s working properly i installed windows 8.1 from CD. Now i am unable to boot Ubuntu. Although Windows is working fine.

I installed Windows 7, which ate Ubuntu's boot file. When starting up the computer, it now goes straight to Windows, without giving me the option of booting Ubuntu.   How can I get Ubuntu back?


Will any divisor of both $a,b>0$ also divide $\gcd(a,b)$? Anyone have a proof of this if it is true, or counter in case of false? thanks,

If $c$ is a common divisor of $a$ and $b$ then $c$ divides the greatest common divisor of $a$ and $b$.  What can we use to prove this?


In comments there's strange behaviour with ending code markup in backslashes. This works just fine here, but not in comments:       First-highlight\-xyzNext-highlight   Instead it overruns as:       First-highlight\-xyzAnother-highlight`   For example:        This should come out as: testing testing\123testing and works just fine here, but in comments it appears as:        Likewise, testing\ works just fine here, but the backslash is ignored in comments and it comes out as just testing.  How do I do this? Or is this a bug?

Is there a way to type something in a comment that renders like this?     You'll need to escape it with a backslash - that is, the \ character.   I've tried various combinations, but a single backslash formatted as code seems to be impossible. Can this be fixed, or can I be enlightened please?  And to clarify: I expect this:  You'll need to escape it with a backslash - that is, the `\\` character.   to work properly, but it doesn't. Instead, one backslash escapes the ` and I'm left with a mess.


Hi guys I just got started with programming and I'm completely fresh to Java. Basically I'm getting a java.lang.NullPointerException error using BlueJ using the startScan() method once I input a value in the console window:  import java.util.*;  public class Machine {     private double balance;     private int count;     private ItemTable Database;     ArrayList<ItemType> items = new ArrayList<>();     ArrayList<ItemType> receipt = new ArrayList<>();      public Machine()     {         balance = 0;         count = 0;     }      public void console()     {         startScan();     }      public void startScan()     {         System.out.println("Enter 'y' to begin, or 's' to shutdown.");          Scanner input = new Scanner(System.in);         boolean shutdown = false;         while (!shutdown)         {             String line = input.nextLine();              if (line.equals("s")){                 shutdown = true;                 System.exit(0);             }              else if (line.equals("y")){                 System.out.println("Enter barcode or press 's' to checkout.");                 scanItem();             }      } }      public void scanItem()     {         Scanner input = new Scanner(System.in);         String line = input.nextLine();         if(Database.barcodeValidate(line))         {             balance += Database.getPrice(line);             count += 1;             receipt.add(new ItemType ("line", Database.getName(line), Database.getPrice(line)));             scanItem();         }          else if(line.equals("s"))         {             finishScan();         }          else         {             System.out.println("Invalid barcode.");             scanItem();         }      }       public void finishScan()     {     for(ItemType i : receipt) {             System.out.println(i.getName() + ", $"+i.getPrice());      }     System.out.println("For "+count+" items scanned, Total price: $"+balance +".");     } }   From another class:  import java.util.ArrayList;  public class ItemTable {      ArrayList<ItemType> items = new ArrayList<>();  public ItemTable()     {         items.add(new ItemType("0", "Orange", 3.50));         items.add(new ItemType("1", "Apple", 2));         items.add(new ItemType("2", "Lemon", 1.50));         items.add(new ItemType("3", "Garbage", 7.50));         items.add(new ItemType("4", "Grass", 20.00));         items.add(new ItemType("5", "Coke", 200));         items.add(new ItemType("6", "Lexus ISF", 120000));         items.add(new ItemType("7", "Lexus is250", 65000));         items.add(new ItemType("8", "Lexus is350", 72000));         items.add(new ItemType("9", "Lexus RC350", 78000));      }          public String getName(String Barcode)     {         for(ItemType i : items) {             if(Barcode.equals(i.getBarcode())) {                 return i.getName();             }             }             return("Invalid barcode");         }      public double getPrice(String Barcode)     {         for(ItemType i : items) {             if(Barcode.equals(i.getBarcode())) {                 return i.getPrice();             }         }         return (-1);     }      public boolean barcodeValidate(String Barcode)     {         if(Barcode.equals("0") || Barcode.equals("1") || Barcode.equals("2") || Barcode.equals("3") || Barcode.equals("4") || Barcode.equals("5") || Barcode.equals("6") || Barcode.equals("7") || Barcode.equals("8") || Barcode.equals("9")) {             return true;         }         else {             return false;         }     }  }   I'm trying to make it so that if the barcode is valid (A string 0-9), the item will be scanned into the machine but keep getting the nullpointer error.

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?


Suppose you are given the digits 1, 1, 2, 2, 3, 3, 4, 4. How would you find the number of 3-digit permutations you can create from those?  For 8-digit permutations the answer should be $\frac{8!}{2!2!2!2!}$ I believe.  However, I cannot think of a way to do this when asked for permutations where not all of the set is used. I have tried $\frac{8P3}{2!2!2!2!}$ but that does not match the amount when I try manually listing all permutations which seems to be 60.  If the problem were to be generalized what would a solution look like?  Thanks in advance.

How many 6-letter permutations can be formed using only the letters of the word, MISSISSIPPI? I understand the trivial case where there are no repeating letters in the word (for arranging smaller words) but I stumble when this isn't satisfied. I'm wondering if there's a simpler way to computing all the possible permutations, as an alternative to manually calculating all the possible 6-letter combinations and summing the corresponding permutations of each. In addition, is there a method to generalize the result based on any P number of letters in a set with repeating letters, to calculate the number of n-letter permutations?  Sorry if this question (or similar) has been asked before, but if it has, please link me to the relevant page. I also apologize if the explanation is unclear, or if I've incorrectly used any terminology (I'm only a high-school student.) If so, please comment. :-)


When reading news titles in English, I always notice a strange form in the title, examples :    Quarantine bringing out creativity for millions on TikTok (source: CNN) Meet the clown lifting spirits in the time of coronavirus (source: CNN)   I said strange because there is no "to be" verb before these 2 verbs ("bringing out" and "lifting"). (I supposed the time is present continuous but with "to be" verb cancellation)  Is it a special form of writing news titles in English?

As my opinion, "no smoking is allowed" must be correct , because it's "passive voice" . Then I saw a title on 9gag.com that was "NO penguins allowed". So what grammar point is here?


Claim: For the continuous function $g:[0,1]\rightarrow[0,1] \exists x \in [0,1]: g(x_1) = x_1$  Proof:  Case 1: If g(0) = 0 and/or g(1) = 1 then g has at least one fix point on one of the ends of the intervall. This means $\exists x_1\in[0,1]: g(x_1)= x_1$  Case 2: Suppose $g(0) \ne 0 $ and $g(1) \ne 1 \Rightarrow$ g does not have a fixed point on one of the ends of the intervall. Therefore we have that g(0) > 0 since (0 < g(0) < 1) and g (1) < 1 since (0 < g(1) < 1) now define:  $$h(x) := g(x) -x$$  $\Rightarrow$ h is continuous since it is constructed by adding two continuous functions. Now:   $$h(0)= g(0)-0>0. \,\,By \,\, g(0)>0$$ $$h(1) = g(1) - 1 < 0. \,\, By \,\, g(1) < 1$$  By the intermediate value thm. $\Rightarrow \exists x_1 [0,1]: h(x_1) = 0$ this implies $\Rightarrow g(x_1)-x_1= 0 \iff g(x_1) = x_1$  Thus $x_1$ is a fixed point of g. By this the claim is proven. q.e.d  Now I'm asking for verification for that proof.

Question: Let $a, b \in \mathbb{R}$ with $a < b$ and let $f: [a,b] \rightarrow [a,b]$ continuous. Show: $f$ has a fixed point, that is, there is an $x \in [a,b]$ with $f(x)=x$.  I suppose this has to do with the basic definition of continuity. The definition I am using is that $f$ is continuous at $a$ if $\displaystyle \lim_{x \to a} f(x)$ exists and if $\displaystyle \lim_{x \to a} f(x) = f(a)$. I must not be understanding it, since I am not sure how to begin showing this... Should I be trying to show that $x$ is both greater than or equal to and less than or equal to $\displaystyle \lim_{x \to a} f(x)$ ?


I have this new Zenbook with the following keyboard config:    If you look carefully in the top right corner, you can see the keys  Home PgUp PgDn and POWER keys  This is driving me crazy, I frequently use the End key but on this keyboard, it is the Power button instead!  From the control panel, I already changed the Power button to do nothing so I don't shutdown my computer inadvertently. But I want my End key back! Is there any way I can get the Power button to act as the End key?  I tried SharpKeys without success as it does not detect that key code...

Forget for a second how bad an idea this would be. But is it possible to remap the power button of a PC or laptop to, say, print some message or anything other than managing the power?  If not, why? Who handles that button, and how low-level such a modification would have to be?  I'm also interested in how the answer changes in the various systems, if it does.


I am building a circuit that involves switching 1000 LEDs via IC drivers. Each IC output has 10 LEDs connected to it, and these are grouped together by their cathodes, in groups of 100, such that only one group is enabled at once. To acheive this cathode switching, I use another IC output, and want to switch it via a transistor that can sink enough power comfortably. Allowing a maximum of 20mA per LED, I need an NPN transistor that can sink 2 amps of current. My circuit runs at 5 volts.  I'm not sure how to get about searching for an appropriate transistor, with so many available. Does anyone know of a parameterised search engine that would allow this? I have come across a couple, but they were overly complicated for someone such as myself who has a relatively basic knowledge of electronics.  If there is no such thing, then a suggestion for my particular use case would also be appreciated. This transistor will be switched by an IC that can supply around 10mA.

I want to control a siren speaker (has a built-in driver) with an Arduino.  The siren needs 12V and consumes about 480mA. The Arduino output pin is 5V and can source 40mA maximum.  I would like to use a transistor to switch the siren on and off. Is this an OK application for a transistor? I'd rather not have to use a relay or a SSR because I don't have any on hand.  Based off of those numbers I calculated my load (siren) resistance to be 25 ohms using Ohms law, R=E/I. (I'm using Amps, Volts, and Ohms as units)  $$\frac{12V}{0.48A} = 25 \Omega$$  I have found various calculations to determine what kind of transistor I need and I'm not quite sure which is the best one. One of them is like this:  $$h_{FE(minimum)} = 5 \times \frac{Load\;Current}{Arduino\;Pin\;Max\;Current}$$  Which gives me a minimum \$h_{FE}\$ of 60.  $$5 \times \frac{0.48}{0.04} = 60$$  This is where I get a little confused. I have a few transistors and their datasheets but I'm not quite sure how to read them. I have read many resources and I am just as confused now as before.  I know I should probably use a NPN transistor but would it matter if I use a PNP instead? Do the same calculations apply? I understand that the circuit changes, active high instead of active low, but are there any drawbacks to PNP over NPN?  The NPN's I have are , ,  and a .   The PNP's I have are ,  and a .  How would I go about choosing the right transistor for the job? I don't want to overload the transistor.


I am a stats rookie and have a relatively basic question regarding the  normal distribution of data.  If I measure a continuous variable under several different conditions/treatments, I look at the distribution of data points separately under each condition and not the whole data set. What if individual treatments are not normally distributed, but others are? Can I, for instance, transform the values of individual treatments to reach a normal distribution in those or would I have to transform the variable for all treatments? I assume the latter, if I want to do more than a pairwise-comparison with a control group or similar. Thank you very much in advance and sorry in case there is an already existing question that goes in the same direction.

I have two dependent variables, one is positively skewed (significantly), the other is negatively skewed (not significant). I can apply a log10 transformation to improve the skewness on the first one.   Questions:   Can I then statistically compare the two variables in a mixed ANOVA test (the two variables are steps of a factor "emotion" and I compare between factor "group"), given that one is transformed and the other isn't?  If not, what options do I have?


Its evident that in the truth table of $p \to q$   When $p$ is False and $q$ is True, Then $p \to q$ is True.  But in some instances i could not convince myself about this truth value.  For example:  $p$: Quadrilateral is Cyclic  $q$: Opposite angles are supplementary  Now is $p$ is False and $q$ is True, how can $p \to q$ can be True?

Provided we have this truth table where "$p\implies q$" means "if $p$ then $q$":  $$\begin{array}{|c|c|c|} \hline p&q&p\implies q\\ \hline T&T&T\\ T&F&F\\ F&T&T\\ F&F&T\\\hline \end{array}$$  My understanding is that "$p\implies q$" means "when there is $p$, there is q". The second row in the truth table where $p$ is true and $q$ is false would then contradict "$p\implies q$" because there is no $q$ when $p$ is present.  Why then, does the third row of the truth table not contradict "$p\implies q$"? If $q$ is true when $p$ is false, then $p$ is not a condition of $q$.  I have not taken any logic class so please explain it in layman's terms.       Administrative note. You may experience being directed here even though your question was actually about line 4 of the truth table instead. In that case, see the companion question  And even if your original worry was about line 3, it might be useful to skim the other question anyway; many of the answers to either question attempt to explain both lines.


Example: Melee character with two handed weapon and wand on belt.  What is available in a round? Can this character draw the wand, use it, then stow it in one round? Effectively using the wand as a ranged attack.  Example: Wizard with two magical staves in a shoulder draw sheath. Can this character swap staves during each round?

I've seen this question asked about 4e, and I think I've found the passage in the 5e PHB that answers the question, but I'd like to make sure I understand this correctly before I impose it on my game.  The question is can sheathing one weapon and drawing another be part of the same "free action", or does this take a full action?  The PHB (page 190)     You can also interact with one object or feature of the environment for free, during either your move or your action. For example [...] you could draw your weapon as part of the same action you use to attack.   If you want to interact with a second object, you need to use your action. Some magic items and other special objects always require an action to use, as stated   in their descriptions.   As a bonus question, what do you think about a Rogue using their "use object" bonus action to draw a weapon after using their free action to sheath one, leaving a standard action and movement action left to be used.


Who else can lift 's hammer?   Thor's hammer is so heavy, I heard only Thor can move or handle it.

I was just watching Ultimate Avengers and apparently, Hulk got really angry and just decided to pick up Thor's hammer... Twice. Now we do know that people other than Thor can wield it as long as they deemed worthy, but I highly doubt that was the case here. So is it canon that Mjölnir has been lifted before just by the Hulk's or any other character's brute strength?


Regardless of whether or not , this secret hat is coveted by many this year for it's sheer coolness. But what is the method of obtaining this hat?

I received some sort of secret hat, the "Chuck Yeager". It says that it is a secret hat. What is the point of a secret hat, besides being fun?  Also it appears that he was the .  Would anyone like to take a guess at why I have this hat?  After reviewing @Michael Hampton's profile I think I know how it is achieved ... but it is still a secret.


I'm not very computer literate, so I need some help with my computer and thought the application will help me to remove the duplicates and other unwanted things from the hard drive. However, I saw many negative reviews on the Net. I'm very frustrated. Thank you!

I see adverts for this particular app all over the place. Is it true that people should stay well away from it, as it could potentially do more harm than good to your Apple Computer, and to your wallet!!


I am a person that's wanted to get into DnD from the moment I've heard about it. There's no groups I know of in my area that play it, and my close by friends don't seem interested, wouldn't know how to play and are generally too busy for this.  I have tried to get into online games with online people, however two of the people I know to be DMS are too busy by this point, and the third has no faith in online play. ( We tried regardless and it failed spectacularly when he failed to show up for around five consecutive sessions.)  I really want to get into this, specifically to play online. I'm scared of trying to do this in person, and don't really think I have much ability to go anywhere. I would be very happy to give any edition a try, but I don't know how to find any group to actually join.

I'd really like to learn how to play pen-and-paper RPGs.  I know that it takes a few players to actually sit down and play, but I'm not at all sure where to find more gamers.  How do I find existing groups to join? Or, are there any resources online that may help me find existing RPG groups or players?


In 5e whats the ruling about arcane casters wearing armour? Does it impact their spellcasting like in earlier editions? I was looking through the book and didn't see anything but I just wanted to be sure, that if I get proficiency it won't be for nothing.

I've just read the , and I'm not sure I'm up to speed regarding casting spells while clad in armor. The only mention I can find about this (page 79):     Because of the mental focus and precise gestures required for   spellcasting, you must be proficient with the armor you are wearing to   cast a spell. You are otherwise too distracted and physically hampered   by your armor for spellcasting.   Does this mean that a character who starts out with a single level fighter (or any other class with heavy armor proficiency) can from then on gain levels as wizard and forever more cast spells, without any penalty whatsoever, while wearing full plate?  I've played all editions of D&D, and this seems both a bit overpowered and very un-D&D-ish to me. Have I missed something?


Scenario 1  Two identical and bilaterally symmetrical cars, driven by identical drivers in the exact center of the car and in the same body position, each traveling the same speed, collide exactly head on. (Essentially, eliminate all variables that would cause rotation or interpenetration during the collision).  Scenario 2  One of the above cars hits an immovable wall instead of an oncoming car.  Question  Will each car in these scenarios experience the same forces? For clarity, the cars in scenario 1 have twice the closing speed of the car and wall in scenario 2.

I was just wondering... I believe that if a car travelling 50 miles per hour crashes into a wall, the result should be the same as crashing to another car also travelling 50 miles per hour (but in the other direction of course)  Is this true? Why is that?


I tried to install turbo c++ using the methods given on this site but every time I run dos box emulator on my Ubuntu 16.04 after typing mount c ~ then I typed C: and then when I typed cd Turbo C++ 3.2.2.0 (the file name which was in my case)  it showed error and said:  try Turbo (sorry space is not included b/w turbo and C)C~1   and again after typing Turbo C~1 it said   unable to change to: Turbo (sorry space is not included b/w turbo and C)C~1   Please help me because I am waiting to see the blue screen of turbo C++ and my coding back!

I am used to Turbo C++ and I am new to Ubuntu.  I really need Turbo C++ to get started.  Can somebody please help me to install Turbo C++ on Ubuntu.


Im NEW to linux . I want to install ubuntu on my laptop , but l'm very confusion about partition scheme , i have searched a lot for this but didn't get any proper , easy and straight forward solution  ..  on my other windows laptop there is thee drive .. One is "C:" .. other one is for my personal use and the third one is for music , movies etc . I want that same THREE partition in ubuntu ..  I have 1TB Hard disk on my machine and i have no plan to run two OS on my same machine .. I want only ubuntu on my machine with three drive ( one for my personal use second one for music and movie etc .. And third one for installing new software and packages like "c:" drive on window ) which cover up all my space .  I want straight forward answer according to my requirement with little explanation  .. Like "root should have 200-300 gb which behave same as "c:" on windows ....  etc ... " .

I'd like to see the full How-To on how to use manual partitioning during Ubuntu installation. The existing guides (at least those I found here) cover only automatic part and leave untouched the manual part (or extremely short and contain no pictures).  I'd like to cover such situations:     If your disk contains other systems:


I'm trying to create a directory which has space in name e.g. "user test" when I fire mkdir -p "user test" it works for me.  When I put "user test" in variable mkdir fails, it creates "user and test" separately  var="user test" mkdir -p $var    I also tried mkdir -p "$var"  Can someone please suggest where I'm doing wrong ?

Or, an introductory guide to robust filename handling and other string passing in shell scripts.  I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some file names).  I encountered a problem such as the following:   I have a file name containing a space hello world, and it was treated as two separate files hello and world. I have an input line with two consecutive spaces and they shrank to one in the input. Leading and trailing whitespace disappears from input lines. Sometimes, when the input contains one of the characters \[*?, they are replaced by some text which is is actually the name of files. There is an apostrophe ' (or a double quote ") in the input and things got weird after that point. There is a backslash in the input (or: I am using Cygwin and some of my file names have Windows-style \ separators).   What is going on and how do I fix it?


Show that there are infinitely many primes $p$ with $$p^5 \equiv 5 \pmod 6$$  I am very confused by this question. I am familiar with Euclid's proof of there being infinitely many primes and can see that most proofs of this nature run along a similar path. For instance, most usually involve assuming a limited number of primes of this type and then multiplying them all together and adding a number to this and this leads to a contradiction later on. For this problem, I have begun by also assuming there are only a finite number of primes with the above property. However, due to the index of 5, I don't see how I can simply multiply all the primes in the finite set together to figure this out. Multiplying two to more numbers with a remainder of 5 on division by six together always leads to a remainder of either 1 if the index is odd and 5 if it is even. I do not know where I can go any further with my analysis. Any hints at how I can tackle this question would be greatly appreciated.

As in the title: Let $q$ be a positive integer, such that for all primes $p$, greater than a given natural number $N_q$, $p \equiv 1 \ \ (\text{mod } q)$. Then $q$ equals 2. I've thought about using some clever fact about the size of $(\mathbb{Z}/p\mathbb{Z})^*$ or $\phi(p)$ but alas nothing seems natural. Any help on how to proceed? Many thanks.


The given problem is the following one.  Find the maximum natural number which is unable to be represented as $17\times x +23\times y \quad x,y\in \mathbb{N}$ .  I've been solving it till following formulas with looking the solution of the problem.  $1\leqq i \leqq 22 \quad 17 \times i \equiv r_i(mod 23)$  $17\times i\not\equiv0(mod23)$  $n(r)=22$  Therefore  we can assume the problem's formula as $(1\leqq x\leqq23 \land y,q\in\mathbb{N})\quad 17\times x+23\times y =23\times q+r\prime \quad\dots(1)$ .  $\uparrow $Because if x is greater than 23,then $17\times x$ is represented as $17\times(23\times t+u)\quad (t\in \mathbb{N,u \in\{1,2,...,23\}})$  $=17\times (23\times t)+17\times u ...(2)$  and $1$st term of $(2)$ is able to be absorbed in $2$nd term of$(1)$.  And my problem begins from here.  The solution says that it is possible to be represented the all natural numbers which are greater than $17\times 23$ with $(1)$and it is impossible to be represented $17\times23$,so the answer is $17\times 23$.  Of course I can deduce that $17\times 23 $ is unable to be represented as a form of $(1)$ but I can't understand that"it is possible to be represented the all natural numbers which are greater than $17\times 23$".  How could this proven?.

I am asked to prove that:       For integers $n, x,y > 0$, where $x,y$ are relatively prime,        every $n \ge (x-1) (y-1)$ can be expressed as $xa + yb$, with nonnegative integers $a,b \ge0$.   How should I approach this? I have very limited knowledge in number theory.


Googling for some information,  came up as a result. The content appears to be an early version of the .  Attribution to SE is not explicitly stated, and at time of writing the page has a copyright notice for an entity sharing the name of the domain. Is this a correct usage of SE content?

of Stack Overflow, all content posted on Stack Exchange sites by their users (i.e. you wonderful people) has been provided to the whole universe under . For my fellow non-lawyers, that license basically means:   Anyone can use any Stack Exchange posts at any time without having to ask for permission Making money off of the copied content is permitted You don't even have to copy stuff from here verbatim; you can just use it as a starting point and make whatever edits you want There are just two rules you have to follow:   You have to provide . Simple links to the original post and author info are just fine. You have to  and allow other people to use your content, as long as they follow these very same rules. How meta!    (If you ever forget any of that, and want to refresh your memory, the license info is linked to in the footer of every page.)  There are, in fact, a lot of people who republish varying amounts of our content for assorted reasons. Unfortunately, there are some Stack Content Republishers Attributing Poorly and/or Excelling at Ranking (SCRAPERs, for short).  In this context, "attributing poorly" means any use that doesn't follow our attribution rules or make any other reasonable attempt at give credit. This can get pretty egregious; I've seen SCRAPERs that not only don't link back to SE originals, but also use fake author info and post dates to make it harder to find originals. By "excelling at ranking," I'm referring to copycat sites that end up higher in Google results than the original SE sites do for the same content. That's not necessarily wrong, but in some cases, it indicates inappropriate SEO hackery.  So, the question is: what can you do if you spot a SCRAPER?


I have some applications crashing.  The message says  The application XXX (process YYY) has stopped unexpectedly. Please try again.  One of applications who is crashing is Google Maps. It is crashing all the time even if I don't run it. Only uninstallation helps.  What does this crashing mean?

Everything was working fine for a long time. But suddenly the device is getting slower than usual (e.g. apps react slowly when starting an action -- like the RSS reader takes "ages" to open an article). Also, several apps start crashing: force-closes as well as unexpected restarts. Sometimes this even involves some automatic reboot of the device.  Is there anything I can do, besides doing a factory-reset? Preferably it should work on un-rooted devices.  Remark: not all described problems may occur together, so on one device e.g. there might be no automatic reboot involved. Question remains the same, nonetheless.


There is russian book,  which is well-known and considered the best comprehensive guide to typography and writing of text in Russian (formatting, margins, font sizes and so on). You can get the idea if you peek my link (even though everything is in Russian).   Is there an American alternative available?

Hum,  I would like to buy myself a book about typography. I have a lot of interest in this field, and already have some knowledge learnt from reading  now and then, among other online sources. I would like to consolidate my knowledge with a book about typography, possibly a mix of theoretical considerations and examples (I quite like the balance achieved, for example, in the Tufte books).


I'm trying to create a function that return an intersect point between two lines. Below is my code.  fn main() {     let line_1: (f64, f64) = (-2.0, 9.5);     let line_2: (f64, f64) = (1.0, -2.0);      let x_1: f64 = (line_2.1 - line_1.1) / (line_1.0 - line_2.0);     let y_1: f64 = line_1.0.mul_add(x_1, line_1.1);      let x_2: f64 = (line_1.1 - line_2.1) / (line_2.0 - line_1.0);     let y_2: f64 = line_2.0.mul_add(x_2, line_2.1);      println!("x_1: {}, y_1: {}", x_1, y_1);     println!("x_2: {}, y_2: {}", x_2, y_2); }   Mathematically x_1 will be equal with x_2 and y_1 will be equal with y_2. Instead, this is the value that's printed.  x_1: 3.8333333333333335, y_1: 1.833333333333333 x_2: 3.8333333333333335, y_2: 1.8333333333333335   The value isn't supposed to have five in it, and y_1 value is different than y_2. Is this some sort of bug, or there's some steps that I miss on handling floating data?

Consider the following code:   0.1 + 0.2 == 0.3  ->  false   0.1 + 0.2         ->  0.30000000000000004   Why do these inaccuracies happen?


So much I don't know.  Would love to be able to ask, learn, and discuss as I do in your other forums.

I have an idea or subject that should have a Q&A, and want to propose a new site. How can I do this?  Related:


No spoilers, please!  My friend and I plan to see Deadpool soon, but she hasn't seen any of the X-Men movies. Would she benefit at all from having seen the X-Men movies (or at least, any specific ones) before Deadpool?

I want to watch Deadpool, but I have heard the character has appeared in X-Men series too. My question is, if I watch X-Men before Deadpool, will it enhance my interest in the Deadpool character?


I came across the following problem that says: Let $A$ be a $3 \times 3$ matrix with real entries.If $A$ commutes with all $3 \times 3$ matrices with real entries,then the number of distinct eigenvalues of $A$  is which of the following:       $ 0,1,2,3$ or none of these.     I do not know how to progress with this particular problem. Can someone point me in the right direction? Thanks in advance for your time.   EDIT:  Even though the question has been asked few months ago and I got some nice explanations ,I revisited the problem and I am little confused about the conclusion of the problem. The scalar matrices of the form $\lambda I$ satisfies the property. So what should be the number of distinct eigenvalues? Here all eigenvalues will be $1$. So,what is the conclusion? Is the answer  $1$ or $0$? Can someone comment on it?

The question is from Axler's "Linear Algebra Done Right", which I'm using for self-study.  We are given a linear operator $T$ over a finite dimensional vector space $V$. We have to show that $T$ is a scalar multiple of the identity iff $\forall S \in {\cal L}(V), TS = ST$. Here, ${\cal L}(V)$ denotes the set of all linear operators over $V$.  One direction is easy to prove. If $T$ is a scalar multiple of the identity, then there exists a scalar $a$ such that $Tv = av$, $\forall v \in V$. Hence, given an arbitrary vector $w$, $$TS(w) = T(Sw) = a(Sw) = S(aw) = S(Tw) = ST(w)$$ where the third equality is possible because $S$ is a linear operator. Then, it follows that $TS = ST$, as required.  I am, however, at a loss as to how to tackle the other direction. I thought that a proof by contradiction,  ultimately constructing a linear operator $S$ for which $TS \neq ST$, might be the way to go, but haven't made much progress.   Thanks in advance!