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copied!<p>The problem might lie <code>printMatrix()</code> and <code>fillMatrix()</code>. <code>clang</code> refused to compile your definition of <code>fillMatrix()</code>:</p> <pre><code>so_mpi.c:22:31: error: use of undeclared identifier 'len' void fillMatrix(int (*matrix)[len], int len){ ^ </code></pre> <p>Dropping <code>len</code> from the prototype just creates another problem:</p> <pre><code>so_mpi.c:26:19: error: subscript of pointer to incomplete type 'int []' matrix[i][j]=j; ~~~~~~^ </code></pre> <p>What did work was this:</p> <pre><code>void fillMatrix(int *matrix, int len) { int i, j; for (i = 0; i < len; ++i) { int *row = &matrix[i * len]; for(j = 0; j < len; ++j) { row[j] = j; } } } fillMatrix((int *)a, MAX); fillMatrix((int *)b, MAX); </code></pre> <p>With that change, everything seems to work fine. I used <code>MAX = 5</code> and 5 nodes. I prefixed logging statements with the node's rank and added a few more logging statements. Here was the result:</p> <pre><code>$ mpirun -np 5 ./so_mpi node 1 of 5 node 4 of 5 node 0 of 5 0: filling matrices 0: matrix B: 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0: matrix A: 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0: broadcast of B complete 0: sending 1 rows (5 elements) of A to node 1 0: sending 1 rows (5 elements) of A to node 2 0: sending 1 rows (5 elements) of A to node 3 0: sending 1 rows (5 elements) of A to node 4 0: matrix A: 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 1: broadcast of B complete 1: received portion of matrix 1: matrix A: 0 0 0 0 0 0 1 2 3 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 node 2 of 5 2: broadcast of B complete 2: received portion of matrix 2: matrix A: 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 0 0 0 0 0 0 0 0 0 0 node 3 of 5 3: broadcast of B complete 3: received portion of matrix 3: matrix A: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 0 0 0 0 0 4: broadcast of B complete 4: received portion of matrix 4: matrix A: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 </code></pre>

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