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POMatrix Vector multiplication in MPI and C
 

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  1. POMatrix Vector multiplication in MPI and C
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    <p>i'm trying to multiply a square matrix by a vector using MPI and C. I must use MPI_Allgather to send all the parts of the matrix to all the processes. This is what i have so far</p> <pre><code>#include "mpi.h" #include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; #include &lt;math.h&gt; #include &lt;string.h&gt; #include &lt;time.h&gt; #define DIM 500 int main(int argc, char *argv[]) { int i, j, n; int nlocal; /* Number of locally stored rows of A */ double *fb; double a[DIM*DIM], b[DIM], x[DIM]; /* Will point to a buffer that stores the entire vector b */ int npes, myrank; MPI_Status status; MPI_Init(&amp;argc,&amp;argv); /* Get information about the communicator */ MPI_Comm_rank(MPI_COMM_WORLD, &amp;myrank); MPI_Comm_size(MPI_COMM_WORLD, &amp;npes); /* Allocate the memory that will store the entire vector b */ fb = (double*)malloc(n*sizeof(double)); nlocal = n/npes; /* Gather the entire vector b on each processor using MPI's ALLGATHER operation */ MPI_Allgather(b, nlocal, MPI_DOUBLE, fb, nlocal, MPI_DOUBLE, MPI_COMM_WORLD); /* Perform the matrix-vector multiplication involving the locally stored submatrix */ for (i=0; i&lt;nlocal; i++) { x[i] = 0.0; for (j=0; j&lt;n; j++) x[i] += a[i*n+j]*fb[j]; } free(fb); MPI_Finalize(); }//end main </code></pre> <p>OK Now it works! It compiles but then i get an mpi allgather internal error! I got this also with other solution i tried.</p> <pre><code>Fatal error in MPI_Allgather: Internal MPI error!, error stack: MPI_Allgather(961).......: MPI_Allgather(sbuf=0xa1828, scount=407275437, MPI_DOU BLE, rbuf=0xf61d0008, rcount=407275437, MPI_DOUBLE, MPI_COMM_WORLD) failed MPIR_Allgather_impl(807).: MPIR_Allgather(766)......: MPIR_Allgather_intra(560): MPIR_Localcopy(357)......: memcpy arguments alias each other, dst=0xb8513d70 src =0xa1828 len=-1036763800 Fatal error in MPI_Allgather: Internal MPI error!, error stack: MPI_Allgather(961).......: MPI_Allgather(sbuf=0xa1828, scount=407275437, MPI_DOU BLE, rbuf=0xf61d0008, rcount=407275437, MPI_DOUBLE, MPI_COMM_WORLD) failed MPIR_Allgather_impl(807).: MPIR_Allgather(766)......: MPIR_Allgather_intra(560): MPIR_Localcopy(357)......: memcpy arguments alias each other, dst=0x3cb9b840 src =0xa1828 len=-1036763800 Fatal error in MPI_Allgather: Internal MPI error!, error stack: MPI_Allgather(961).......: MPI_Allgather(sbuf=0xa1828, scount=407275437, MPI_DOU BLE, rbuf=0xf61d0008, rcount=407275437, MPI_DOUBLE, MPI_COMM_WORLD) failed MPIR_Allgather_impl(807).: MPIR_Allgather(766)......: MPIR_Allgather_intra(560): MPIR_Localcopy(357)......: memcpy arguments alias each other, dst=0x7a857ad8 src =0xa1828 len=-1036763800 </code></pre> <p>Can anyone help me?</p>
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      1. POMatrix Vector multiplication in MPI and C
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    1. CO`a` is a two-dimensional array, but you're accessing it like it only has one dimension. The syntax would be `a[??][??]` rather than `a[??]`, but what you put in place of the ??s depends on your data layout.
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    2. COi'm acessing it like one dimention because it is broken up through rows in the diferent processes.
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    3. COI've tried that but still gives me that error. Don't know how to turn this arround
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      1. USMário Santana
 

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