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What's the best way to communicate between view controllers?
Why does factoring eliminate a hole in the limit? $$\lim _{x\rightarrow 5}\frac{x^2-25}{x-5}  = \lim_{x\rightarrow 5} (x+5)$$  I understand that to evaluate a limit that has a zero ("hole") in the denominator we have to factor and cancel terms, and that the original limit is equal to the new and simplified limit. I understand how to do this procedurally, but I'd like to know why this works. I've only been told the methodology of expanding the $x^2-25$ into $(x-5)(x+5)$, but I don't just want to understand the methodology which my teacher tells me to "just memorize", I really want to know what's going on. I've read about factoring in abstract algebra, and about irreducible polynomials (just an example...), and I'd like to get a bigger picture of the abstract algebra in order to see why we factor the limit and why the simplified is equal to the original if it's missing the $(x-5)$, which has been cancelled. I don't want to just memorize things, I would really like to understand, but I've been told that this is "just how we do it" and that I should "practice to just memorize the procedure." I really want to understand this in abstract algebra terms, please elaborate. Thank you very much. Adjusting space between array rows and columns Is it possible to use `find -exec sh -c` safely? I'm trying to use find to echo 0 into some files, but apparently this only works with sh -c:  find /proc/sys/net/ipv6 -name accept_ra -exec sh -c 'echo 0 &gt; {}' \;   But using sh -c with find -exec makes me feel very uneasy because I suspect quoting problems. I fiddled a bit with it and apparently my suspicions were justified:   My test setup:  martin@dogmeat ~ % cd findtest  martin@dogmeat ~/findtest % echo one &gt; file\ with\ spaces martin@dogmeat ~/findtest % echo two &gt; file\ with\ \'single\ quotes\' martin@dogmeat ~/findtest % echo three &gt; file\ with\ \"double\ quotes\" martin@dogmeat ~/findtest % ll insgesamt 12K -rw-rw-r-- 1 martin martin 6 Sep 17 12:01 file with "double quotes" -rw-rw-r-- 1 martin martin 4 Sep 17 12:01 file with 'single quotes' -rw-rw-r-- 1 martin martin 4 Sep 17 12:01 file with spaces  Using find -exec without sh -c seems to work without problems - no quoting necessary here:  martin@dogmeat ~ % find findtest -type f -exec cat {} \; one two three  But when I'm using sh -c {} seems to require some kind of quoting:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c 'cat {}' \; cat: findtest/file: No such file or directory cat: with: No such file or directory cat: spaces: No such file or directory cat: findtest/file: No such file or directory cat: with: No such file or directory cat: single quotes: No such file or directory cat: findtest/file: No such file or directory cat: with: No such file or directory cat: double quotes: No such file or directory  Double quotes work as long as no file name contains double quotes:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c 'cat "{}"' \; one two cat: findtest/file with double: No such file or directory cat: quotes: No such file or directory  Single quotes work as long as no file name contains single quotes:  martin@dogmeat ~ % LANG=C find findtest -type f -exec sh -c "cat '{}'" \; one cat: findtest/file with single: No such file or directory cat: quotes: No such file or directory three    I haven't found a solution that works in all cases. Is there something I'm overlooking, or is using sh -c in find -exec inherently unsafe? Which serial protocol or encoding scheme does this scoreboard use? I am trying to decode a signal stream coming from a Nevco scoreboard controller:    Packets like this are sent every ~2.7 ms.  I suspect it is some sort of UART signal because it is on the RX line of a ATMEGA48, but I cannot identify the finer protocol details like parity and stop bits. All the combinations I have tried returns junk data, so it may be another encoding scheme.  What's unusual is that the same signal is also sent to the MOSI pin of the microcontroller, but there is no clock signal anywhere.  A .vcd file is .   The shortest pulses (both high and low) are always 8us in length.    This is what two packets look like. Anyone got ideas? One of our SQL Server 2014 database transaction logs is growing very fast and I cannot find the root cause for this.  Database in Simple recovery mode. During full backup the log file grows to its limits (800GB) and backup fails.  I checked the transactions during the backup and did not find anything strange.  All transactions are our regular loading and no maintenance jobs (index rebuilds etc.)  I am aware of that backup keep the log from reuse but this mean 800GB changes during the backup period and this does not make any sense.  I had compared this DB to similar DB size, loading and backup duration. The second DB Log is not growing more than 400GB.  DB size is 7TB. Backup time is ~20H. The only time log is growing is during backup. Log_reuse shows correct Backup_Restore. No long running transactions.  The problem is the "speed" of log growth - compared to similar sites with same load and same backup duration, the log is 4 time less. I find myself repeating a lot of:  mkdir longtitleproject cd longtitleproject   Is there a way of doing it in one line without repeating the directory name? I'm on bash here. Why does Boolean.ToString output "True" and not "true" true.ToString()  false.toString();  Output: True False   Is there a valid reason for it being "True" and not "true"? It breaks when writing XML as XML's boolean type is lower case, and also isn't compatible with C#'s true/false (not sure about CLS though).  Update  Here is my very hacky way of getting around it in C# (for use with XML)  internal static string ToXmlString(this bool b) {     return b.ToString().ToLower(); }   Of course that adds 1 more method to the stack, but removes ToLowers() everywhere. How can I find the points at which two circles intersect? Given the radius and $x,y$ coordinates of the center point of two circles how can I calculate their points of intersection if they have any? Is the uncertainty principle just saying something about what an observer can know or is it a fundamental property of nature? I ask this question because I have read two different quotes on the  that don't seem to match very well. There are similar questions around here but I would like an explanation that reconciles these two interpretations specifically:   Feynman talks about the uncertainty principle in one of his lectures and mentions it as the reason why electrons don't crash into the atom's nucleus: If they did they would have an exact location and momentum which is not allowed by the uncertainty principle. In saying this it is clear that the uncertainty principle is a fundamental property of nature because it has an effect on where an electron can reside. Recently I read - somewhere else but I forgot where exactly - an account of the uncertainty principle where there was explained how we can measure position of a particle by firing another particle into it, the collision disturbs the velocity of the observed particle therefore we can not know its momentum anymore.   Now, 2) very much seems like a limitation of what the observer can know, while 1) attributes a fundamental property of nature to it (electrons don't crash into the nucleus). What is the correct way to think about this? Ok... so this is embarrassing.  I typed in "boobs" on EncyclopediaDramatica's search because, well, it's a really funny page.  But now I've got a problem... EVERY TIME I click a search field in Chrome now, it shows "boobs" as the first suggestion in the drop down!  This is not really socially acceptable as this laptop goes with me everywhere and Chrome is my primary browser.  Is there a way I can isolate and remove just that one entry? How do I create a script file for terminal commands? In Windows I can write a file containing commands for cmd (usually .cmd or .bat files).  When I click on those files it will open cmd.exe and run them commands the file contains.  How would I do this in Ubuntu?         I'm sure this is a duplicate, but I can't find my answer. Its similar to these questions, but they don't answer the question: Shouldn't the Terms of Service use Stack Overflow, Inc.? The  still uses the term Stack Exchange, Inc. However, I believe that the name is now Stack Overflow, Inc. , so I believe that should be changed to that. It is weird to have the wrong name in a legal document.   Yes, I actually read the Terms of Service. You should also do that. I tried to use the usb-creator.exe from Ubuntu 10.10 desktop i386 ISO image and it does create an USB stick that doesn't boot. When I try to boot from it I get:     Operating System not found.   I try to do this from Windows 7 x64. I'm not looking to create a live Ubuntu media, only an installation USB disk.  I repeated the process several times and I even tried to reformat the USB drive (FAT32), no success yet.  The USB stick is a 8GB one. I am a Ph.D. dropout with a one year of career gap. I want to return to academia, but now  I have realized that it was perhaps the biggest mistake to take a gap after quitting my Ph.D. The purpose of taking a gap was to work on my communication skills and get a  new perspective on my work and my career in science. This could have been done within a period of 2-3 months but it became one year long because of my own recklessness. I allowed myself to distract from my goal and I started working on my hobby i.e. Painting. I lost myself there and completely lost track of my time. I was really enjoying everything about this new venture. I took it as a challenge to become better at my skills in painting. Eventually, I became the best in my group and got lots of appreciation. But then, I lost my interest while realizing that there was no further challenge and all there was left is to work and work while crafting your art which was never going to be perfect. It made me realize that what I actually love is to take the new challenges and work on myself. To be an artist was never a career option for me, all I wanted was to learn the skills. That's it!   While counting my achievement in science, I  realized that it was an irresponsible thing to take a gap in doing something that has nothing to do with science. Earlier I had a scholarship and a very competitive mind that has led me to get a Ph.D. position in one of the best labs in the country. Now I don't have the scholarship. I want to go back to my world of research where I was accelerating exponentially. I want to tackle the challenges of science with a new perspective and better skills. I want to be productive more than earlier and ready to take all the tough challenges.  But I feel embarrassed about my past mistake. Because of this, I come across as someone who is not sincere about her career. But I can't help it because the truth is that I did behave insincerely by losing track of my time.  I should have been conscious enough to realize the consequences. Now, what do I do? The past has gone and the vision of the present is crying for a better future. How do I make things better like before? Sum of reciprocals of numbers with certain terms omitted What's a big-vocabulary word for someone with a big vocabulary?  I'd like to say I'm looking for a "_____". In indirect speech we generally backshift the tense. For ex - Direct speech : "I am the most powerful person." Indirect speech : "He said that he was the most powerful person."  What if someone reports like -  He denied the charges claiming that he is/was the most powerful person. So here which is correct- is or was ?  Thanks in advance. How to make a good glow effect around a sun? Why does latex stretch small sections across the whole page vertically? Adding related resources or hyperlinks in edits So, I've been rejecting the addition of resources/hyperlinks to posts simply because I had no idea that this was an acceptable practice.  Today, I was browsing through the edits page and saw:     Some common reasons to edit are:         to fix grammatical or spelling mistakes   to clarify the meaning of a post without changing it   to correct minor mistakes or add addendums / updates as the post ages   to add related resources or hyperlinks      Why is this an acceptable practice?  I can see adding links to official documentation, but the quality of outside resources is (potentially) subjective.  I see the merit in adding resources, but it seems to me that these additional resources should be placed in comments, not inserted into the post via an edit.  Anyone have thoughts on this?