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POSending blocks of 2D array rows using MPI in C
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  1. POSending blocks of 2D array rows using MPI in C
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    copied!<p>I am trying to do a matrix multiplication using MPI in C. (c &lt;= a*b)</p> <p>I am running the following code on 4 nodes. All the matrices are 8*8 in size. </p> <pre><code>(num of rows in a matrix % num of nodes == 0) </code></pre> <p>matrix b[][] is broadcast so all the nodes get the same copy. For matrix a[][], instead of broadcasting, I want to send only the set of rows that is needed by each node. </p> <p>But when I run the following code and print the matrix a[][] after MPI_Recv() worker nodes print 0s instead of the values assigned in the master node.</p> <p>Can you point out what am I doing wrong here?</p> <pre><code>#include &lt;stdio.h&gt; #include "mpi.h" #include "matrix.c" // matrix definitions and matrix operation functions are here int main(int argc, char *argv[]) { MPI_Status status; int num, rank, size, tag, high,low,i; int offset, tmphigh,rows; MPI_Init(&amp;argc, &amp;argv); MPI_Comm_rank(MPI_COMM_WORLD, &amp;rank); MPI_Comm_size(MPI_COMM_WORLD, &amp;size); rows=MAX/size; // MAX is the length(=height) of the matrices tag = 201; low=rank*rows; high=low+rows; if (rank == 0) { fillMatrix(b,MAX); fillMatrix(a,MAX); } MPI_Bcast(&amp;b[0][0],MAX*MAX,MPI_INT,0,MPI_COMM_WORLD); if(rank==0){ for(i=1;i&lt;size;i++){ offset=i*rows; MPI_Send(&amp;a[offset][0],rows*MAX,MPI_INT,i,tag,MPI_COMM_WORLD); } }else{ MPI_Recv(&amp;a[low][0],rows*MAX,MPI_INT,0,tag,MPI_COMM_WORLD,&amp;status); } printMatrix(a,MAX); MPI_Finalize(); return 0; } </code></pre> <p>here is how matrices are created</p> <pre><code>int a[MAX][MAX], b[MAX][MAX], c[MAX][MAX]; int len; //(edited after Jeremy W. Sherman's comment ) //this was the reason that caused this problem. changing this to int len=MAX; solved the problem void fillMatrix(int (*matrix)[len], int len){ int i=0,j=0; for(i=0;i&lt;len;i++){ for(j=0;j&lt;len;j++){ matrix[i][j]=j; } } //printMatrix(matrix,len); } </code></pre> <p>Thank You.</p>
 

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