I am trying to learn C++, but I can't even make the first (hello world) example from cplusplus.org work with g++ command or c++. I created a file just like the example and ran g++ myfile, then ./myfile.  I get a permission problem, then I use chmod +x myfile and the permission problem is gone but this problem happens:  gzuspower@gzuspower:~/Desktop$ ./4 ./4: line 1: //myfirst: No such file or directory ./4: line 4: syntax error near unexpected token `(' ./4: line 4: `int main ()'   I called my file 4 because it is my 4th attempt. This is on Xubuntu 16.04.The duplicate question answer did not work i tried .c ,.cpp ,as file extension and tried firstc++ (my first attempt file) instead of 4(my fourth attempt file) and nothing works. i'm going to try different form of hello-world code.
I am  new to Linux. I am using Ubuntu 11.04 and do not know how to compile and execute C++ program in it. I need to know the commands to Compile and Execute a C++ program in Linux.
What happens to waves when they hit smaller apertures than their wavelenghts? Proving that the Hopf map $S^3 \to S^2$ is a submersion I need to show that the Hopf map $H : S^3 \to S^2$ is a submersion. There are many ways to define it, but for now I've gone with the restriction of the function $F : \mathbb{R}^4 \to \mathbb{R}^3$ mapping $$(x,y,u,v)\mapsto (2(xu+yv), 2(xv-yu), x^2+y^2-u^2-v^2).$$ It wasn't too bad to show that $F$ is a submersion, but is there a way to go from here to show that $H$ is a submersion? I can write down $H$ as the composition $$S^3 \overset{\iota}{\hookrightarrow} \mathbb{R}^4 \overset{F}{\to} \mathbb{R}^3 \overset{\pi}{\to} S^2,$$ and define $\pi(p) = p/\lVert p\rVert$, but I don't really know where to go after computing the Jacobian of $\pi$, and I don't know if this will even work for my purposes (I don't see how to argue that the composition of the corresponding differentials here isn't rank $1$ — I know $d\iota$ has trivial kernel but things seem to break down once I get to $d\pi$). I'm really just trying to avoid having to compute the Jacobian of $H$ with respect to the stereographic projections and show that that beast of a thing is full rank. Am I on the right track, or is there a better way? Where should I post my sum-up of the answers, as the OP? Sometimes as the OP (question asker), after reading through all the answers, I have my own sum-up about them. I want to tell people and all further readers about my feeling and comprehension about my desired answer and how all the answers helped towards solving my problem.  Where's the correct place to put that information? Things I've considered:   Edit into my question: No because that's not part of the question A comment under the question: I dislike that due to limited formatting in comments and its subject to removal (though the latter won't be the case) A comment under the highest-scored or the accepted answer: Still the same reason above. This is, for the time being, the place I'm posting that. A separate answer: Those thoughts probably don't qualify as an answer Rep value on the new flair is not updated There is an update issue with the new flairs. Yesterday I replaced all my flair snippets with the new ones, but the rep value on the "default theme" has not been updated. Here is a screeny:    The other themes show the correct value whereas the default one does not. Solving linear congruence (modular inverse or fraction) via gcd Bezout equation Isn't finding the inverse of $a$, that is, $a'$ in $aa'\equiv1\pmod{m}$ equivalent to solving the diophantine equation $aa'-mb=1$, where the unknowns are $a'$ and $b$? I have seem some answers on this site (where the extended Euclidean Algorithm is mentioned mainly) as well as looked up some books but there is no mention of this. Am I going wrong somewhere or is this a correct method of finding modular inverses? Also can't we find the Bézout's coefficients by solving the corresponding diophantine equation instead of using the extended Euclidean Algorithm? Where are executables for programs stored in Ubuntu?  An application (Komodo Edit) is asking me to identify an application to be used as a web browser. I've become used to just entering the application name as a command for situations such as these, but this scenario got me thinking.   I know in Windows it would just be the relevant application folder in the 'program files' folder, but I'm assuming things are a bit different on Linux?  I thought somewhere like bin would be logical but this appears to standard Linux/Unix applications. Where would I find the binary executable for applications stored on my system? Java Command line arguments I am trying to detect whether the 'a' was entered as the first string argument. Java Round up Any Number Short story in book collection about war machines and armies out of control I read in an anthology book in 1975. It starts with two people watching a “robot” plane glide high and then dive into an opening of a factory causing a massive explosion. I’m not sure but I think the people may have orchestrated the attack on purpose to get the robot armies fighting each other in the hope that it would diminish robot army capabilities and bring them under control. The robot wars did occur, but at the end of the story the people discover a tube sticking out of the ground that is periodically shooting something into the air. Nearby they find a canister that did not get launched out of the “cannon” successfully and it was broken open. After close examination they discover tiny “ants” on the canister that are actually tiny robots which are rebuilding the robot war factories. The robots have adapted and will keep trying to fulfill their mission. This story may  have been in a booked edited by Roger Elwood, but I cannot guarantee it. Some Data Failed to Reconstruct, Motion Tracking I added tracks and stuff, but then when I tried to solve motion track, there was a error that said:     Some Data Failed to Reconstruct   and it also said to look into the console for details, which I did. This is what the console said:    By my understanding, my video is 372 frames long, and Blender is cutting the footage at 318 for some reason. Here is the image of the scene:    Why? Here are links to  and also . Also the next morning I did a camera solve, but then most of the frames went red. Login screen resolution So I just installed Ubuntu 16.04 on my Dell XPS 13. When I get to the login screen it starts at 3200x1800 for a quick second, then I get a way lower resolution like 800x600 but as soon as I login it adjusts to 3200x1800. How would I get 3200x1800 permanently on my login screen? I didn't have this issue on 14.04. Before running a ridge regression model, do I need to preform variable selection? I am currently constructing a model that uses last year's departmental information to predict employee churn for the current year.  I have 55 features and 318 departments in my data set.  A good portion of my independent variables are correlated, and because of this, I believe that performing a ridge regression on my data will lead to optimal predictions when I bring the model into production.  I have studied ridge regression and understand that the lambda coefficient computed for a given predictor can minimize the effect that predictor has on the model to next to nothing.  Does this mean that performing a ridge regression means I don't have to bother with variable selection? If I do need to perform a variable selection technique, would implementing a stepwise regression and then using those selected variables in my ridge regression be a valid approach at variable selection? I already posted this question on stack exchange but was informed that stack exchange was the better platform to ask statistical questions.  I am sorry for the confusion. Motivation for Ramanujan's mysterious $\pi$ formula The following formula for $\pi$ was discovered by Ramanujan: $$\frac1{\pi} = \frac{2\sqrt{2}}{9801} \sum_{k=0}^\infty \frac{(4k)!(1103+26390k)}{(k!)^4 396^{4k}}\!$$   Does anyone know how it works, or what the motivation for it is? Is there a way to see who voted on your posts? Is Tactical Down-Voting ever valid? Has anyone noticed any tactical downvoting of their, or other people, answers?  For example, in a recent answer to a question, my answer described a possible solution.  Shortly afterwards, another answer appeared following the solution I had mentioned.    I know that this is completely in the spirit of the site, however my answer had been down voted even though it was still as valid as it ever was.  Another poster also had his equally valid solution down voted.  There is no way of knowing the reason behind the down voting, as no comments were left, but I am suspicious as to the ethics behind down voting someone else's valid answer in the hope of making their own answer more prominent.  Are people really that desperate to gain reputation?  I have seen comments in other posts that suggest that tactical downvoting has occurred.  So, does anyone think that it is acceptable to downvote another post, even though it is still correct but may not provide a complete answer, to make their own appear more favourably? Filling only when one curve is below the other Having trouble creating an array of objects Given two input layers  The clip layer - an arbitrary layer (though in my case it's a float 1 band geotiff) The mask layer - a paletted raster in which every pixel is either NO DATA or a single &quot;color&quot; value, same for every pixel.  I want to create an output raster whose overall extent matches the extent of the mask layer and each pixel is either NO DATA if the corresponding pixel of the mask layer is NO DATA or the value of the corresponding pixel from the clip layer if the corresponding pixel of the mask layer is not NO DATA. I know I can mask the clip layer with a polygon, but the mask layer is a raster. Polygonizing the raster layer is possible in principle, but would result in a polygon with a lot of very short edges. Is there a direct way to do this in QGIS? I suppose there's probably a path that involves creating a new layer and using the raster calculator, but I'm hoping there's something more direct. Further complicating the matter is that the two rasters might not have the same resolution and origin. I believe this is equivalent to  in ArcMap. My sisters and I all have iPhones under the same account. I also have an iPad under the same account. I am trying to get the iMessage on my iPad compatible with my phone number, not email address.   The only phone number choice to choose from is my sister's iPhone number. How can I choose my phone number for iMessage on my iPad? Is it possible for information (like 1 and 0s) to be transmitted faster than light?   For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them starts pulling and pushing on his/her end.   The person on the opposite end should receive the pushes and pulls instantaneously as no particle is making the full journey.  Would this actually work?