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POSending 2D Int Array with MPI_Send and Recv
 

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  1. POSending 2D Int Array with MPI_Send and Recv
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    <p>I am trying to send a 2D integer array of arbitrary length from slave processes to the master but I keep getting a segmentation fault. As MPI is quite difficult to debug, I'm not certain that the issue has to do with the send/recv but if it's not that then it will have to be with the way I am allocating the arrays themselves.</p> <p>I followed a previous question on here in regards to ensuring that the memory allocated to the array is contiguous but that still didn't fix the segmentation fault.</p> <p>Below are some sections of my code:</p> <p>Create array:</p> <pre><code>int** create2DArray(int sizeX, int sizeY) { int* data = (int *) malloc(sizeX * sizeY * sizeof(int)); int** array= (int **) malloc(sizeX * sizeof(int*)); int i; for (i=0; i&lt;sizeX; i++) { array[i] = &amp;(data[sizeY * i]); } return array; } </code></pre> <p>Initialise arrays:</p> <pre><code>if(rank==0) { display = x11setup(&amp;win, &amp;gc, width, height); pixels = create2DArray(X_RESN, Y_RESN); } else { xStart = xPixels * (rank - 1); xFinish = xStart + xPixels; pixels = create2DArray(xPixels, Y_RESN); } </code></pre> <p>Send:</p> <pre><code>MPI_Send(&amp;pixels[0][0], xPixels * Y_RESN, MPI_INT, 0, type, MPI_COMM_WORLD); </code></pre> <p>Recv:</p> <pre><code>for(i = 1; i &lt; processes; i++) { int** pixelChunk = create2DArray(xPixels, Y_RESN); MPI_Recv(&amp;pixelChunk[0][0], xPixels * Y_RESN, MPI_INT, i, type, MPI_COMM_WORLD, &amp;status); int xStart = xPixels * (i - 1); int xFinish = xStart + xPixels; int k; for(j = xStart; j &lt; xFinish; j++) { for(k = 0; k &lt; Y_RESN; k++) { pixels[j][k] = pixelChunk[j - (xPixels * i - 1)][k]; } } } </code></pre>
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    1. COExactly which operation results in a segfault?
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    2. COYour code seems a bit complex, i.e. We don't see here where `xPixels` come from for example. Have you tried simplifying the code to only sending a fixed array, receiving it and trying to make sure that it is transmitted correctly? The sending/receiving code looks legit.
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    3. COAre you sure that `X_RESN` is dividable by `processes - 1`?
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