Examining each connected pixel to select its neighbors to separate clusters using ArcGIS for Desktop?
Comparing areas in scanned historical land use maps using QGIS?
Prove $ \sin(A+B)\sin(A-B)=\sin^2A-\sin^2B $ How would I verify the following double angle identity. $$ \sin(A+B)\sin(A-B)=\sin^2A-\sin^2B $$ So far I have done this. $$ (\sin A\cos B+\cos A\sin B)(\sin A\cos B-\cos A\sin B)  $$But I am not sure how to proceed. How to Give Credit for An Answer in the Comments I asked a question on SO and someone gave me the answer as a comment to the question. Subsequently, someone else gave the same answer as an answer.  I would like to give credit to the poster who made the comment. Is there any way to do that?   Being new to the site, my only thought would be to contact the commenter and tell him to post an answer if he/she wants credit. Can I control voltage of USB data pins? I just bought a 5 volt dual relay module for my arduino.  But now that I have it I was wondering if there is any way that I could control it directly from USB.    The pinout of the module is GND  ONE  TWO  VOC This would make it really easy to just connect a USB cable to it. Assuming I did that is there any way to send 5 volt through the USB Data+ and Data-?  Thank you Distribution of number of Bernoulli trials to a given number of successes As a new user without much rep, what should I do if someone else has already asked a question I have, but it has no answers? Suppose you had a question, and you really want a good answer that would solve your problem, but noticed it was already asked by someone else. However, no one has posted any answers. The question is technically considered "unanswered", but a lot of users who would otherwise bother to give a correct answer probably skip the question completely for some reason.  What should I do in this case?  One idea is to ask a new, completely identical question, in the hope users will notice the new question and post an answer there. But would that go against SE policy?     Note: This is adapted from , but that doesn't cover the case where the original question is unanswered. Also, it is not a duplicate of , as that question asks about getting attention for one's own questions, while this one and the one linked above ask about getting an answer if someone else has already posted the same thing. Is color undefined I want to check whether a color has been previously defined, consider the below code which doesn't execute.  \documentclass{article}  \usepackage{xcolor} \newcommand{\colorprovide}[2]{\ifx\undefined{#1}\colorlet{#1}{#2}\fi}  \begin{document}     %Initial Definition     \colorprovide{mycolor}{red}     \textcolor{mycolor}{Test 1}      %Will overwrite     \colorlet{mycolor}{green}     \textcolor{mycolor}{Test 2}      %Should NOT overwrite as it exists     \colorprovide{mycolor}{red}     \textcolor{mycolor}{Test 3} \end{document}   In other words and analogous to \providecommand{...} not renewing an existing command if it exists, I need a macro which will will NOT redefine a color if the color has already been defined.  The above code throws an error as the logical checking part \ifx\undefined... is incorrect. What's the best way to find the inverse of datetime.isocalendar()? Why does correlation matrix need to be positive semi-definite and what does it mean to be or not to be positive semi-definite? I have been researching the meaning of positive semi-definite property of correlation or covariance matrices.   I am looking for any information on   Definition of positive semi-definiteness; Its important properties, practical implications; The consequence of having negative determinant, impact on multivariate analysis or simulation results etc. Wires do not connect in Circuitikz I've been trying to use relative coordinates to make my drawings more precise but it seems I don't know how the command \node works since I've been having this problem while connecting a circuit element to another:    I'm trying to eliminate the blank between the two wires.  This is the minimal code:  \documentclass{book} \usepackage[siunitx,RPvoltages]{circuitikz} %Circuit Schematics/Diagram \usetikzlibrary{arrows,shapes,calc,positioning} \begin{document}     \begin{circuitikz}             \path (0,0) coordinate (C);             % Comparatore             \path (C) + (0,-1) + (1,0) coordinate (com) node[above]{};             \path (com) + (1.5,-1) node[op amp] (comp) {};             % Collegamenti Comparatore             \node (G1) at ([shift=({-1.3cm,0cm})]comp.-) {};             \draw (G1) -- (comp.-);             \node (G2) at ([shift=({-1.3cm,0cm})]comp.+) {};             \draw (G2) -- (comp.+);             \draw (C) -- (G1); % Collegamento Rettificatore - Comparatore         \end{circuitikz} \end{document}   Thanks for any help! Dynamically reformatting man pages on terminal dimension changes One common workflow of mine is to open a manual page in a terminal, then another terminal in which to test things. The man page is formatted to the initial dimensions of the first terminal. When I now resize my windows (or have my WM do that for me automatically), there is either a gap to the right of the preformatted page, or lines wrap. At this point I usually q(uit) and !! (run again), which loses my position in the page.  I assume the formatting process is quite CPU intensive, or maybe it stems from ancient times of fixed terminal sizes. The less pager dynamically reacts to terminal resize events, so it should be possible in theory.  I tried perusing man pages, searching the Web, asking on IRC -- the whole lot -- but couldn't come up with anything.   Can I trigger reformatting from within or outside of the man utility? Is there a version of the man utility that resizes the page dynamically?  Is there way to customize some part of the formatting/display process to make it update on SIGWINCH? See YouTube videos in Anaglyph mode How to see a YouTube video in  from a non-3D Android device? I am not able to enable Anaglyph mode from the YouTube application. Dollar cost averaging - Should I still do it if I have a large pile of cash now? I currently have a large pile of cash savings ($240,000) which I really should have been investing all this time, but the past is past and no point dwelling on it.  I am currently 38 years old (2 kids. Wife who is also a high earner - $100,000), with a high salary ($150,000). I have read "The Intelligent Investor" and am really sold on dollar cost averaging as a strategy, using the index funds offered by Vanguard.  My current dilemma is what to do with the cash I already have. My current plan is to still follow the dollar cost averaging and slowly move it into vanguard over a period of 4 years (~$5000 per month). While leaving the remaining parts of the cash in term deposits. So $50,000 in a 3 year term deposit at 3%, $50,000 in a 2 year term deposit at 2.8% etc.  But in someways it feels overly conservative. Should I just move all the money now? Or perhaps in a shorter time frame (3 years? 2 years? 1 year?).  There are a few other questions on the site similar to mine, but they are from 2013/2014 etc. Given that currently the stock market is at a high and there is a lot of economic uncertainty on the horizon, putting everything in the stock/bond market at once now seems like a risky move. And it seems to violate the principle of dollar cost averaging. Or am I violating dollar cost averaging by trying to "time the market" by looking at it's current value?  Reading this section  seems to indicate that I should just invest everything now. But the first paragraph also seems to suggest giving more weight to that advice if the market was trending upwards (Which I am not certain the current market is/will be for long).  PS: My current investment horizon is long. Basically retirement, about 20 years from now. After T-2, why not send back another T-800? I'm being forced to use my Macbook more and more with my metered 4G connection. I really need to keep data usage limited. Windows has an  mode which really helps with this.   What's the best way to handle this issue in the OSX world? Perhaps some use of the firewall? Is there any sort of logging happening as to what is using the network?  Thanks for your help :-) How do you update an Excel file (Data Refresh and update formulas) WITHOUT opening the file? I have an Excel file that want to update and save automatically with out having to open it or manually interact with.  Manually, I open the file up and hit data refresh which goes and does a SQL query and then hit F9 for the formulas to update and then I just close/save.    (I then would mail the file out to people using a perl script or use SAS JMP to run some numbers/charts and also mail them out.  Basically I need to script some things which require the XLS file to be updated.) How do I search a specific user's answers? How to read the following Itinerary What do the abbreviations mean in the following itinerary:     2  EK 641 L 29NOV 2 KBLDXB HK1       I  1630 1905   *1A/E*                      3  EK 344 L 29NOV 2 DXBKUL HK1       3  2140 0835+1 *1A/E*                      4  MH 704 V 30NOV 3 KULMNL HK1       M  1245 1630   *1A/E*                      5  UA 184 Y 01DEC 4 MNLGUM HK1       1  2255 0440+1 *1A/E*                      6  UA 155 Y 02DEC 5 GUMTKK HK1          0820 1008   especially, the numbers (2,2,3,4,5) before KBLDXB, KULMNL.... The letters and numbers before time (I, 3, M, 1) *1A/E*? Does $\sum_{n=1}^{\infty} \sin(\pi(2+\sqrt{3})^n)$ converge? Converge absolutely? Per the title, does $\displaystyle\sum_{n=1}^{\infty} \sin(\pi(2+\sqrt{3})^n)$ converge? Converge absolutely?   I'm stuck on this question, not sure how to approach it.  Thank you! Massive spam users and spam entries despite triple layer protection The level 4 spell Polymorph requires concentration to maintain.  The subject retains their personality and alignment, but they have the mental statistics of the new form, which must be a beast and cannot speak or cast spells.  If a caster targets themselves with this spell, can they concentrate to maintain it, or does this depend on the mental statistics of the beast form they choose?  This situation certainly occurs in practice, since Wizards reaching level 10 in the School of Transmutation gain the Shapechanger feature.  This allows them to cast Polymorph, but only upon themselves and only to change into a beast of CR 1 or lower.  Beasts with CR 1 or less range in Intelligence from the Giant Eagle (Int 8) to the Frog (Int 1).