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<title>GNU Scientific Library – Reference Manual: BLAS Examples</title>
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<a name="Examples-7"></a>
<h3 class="section">13.2 Examples</h3>
<p>The following program computes the product of two matrices using the
Level-3 <small>BLAS</small> function <small>DGEMM</small>,
</p>
<div class="example">
<pre class="example">[ 0.11 0.12 0.13 ] [ 1011 1012 ] [ 367.76 368.12 ]
[ 0.21 0.22 0.23 ] [ 1021 1022 ] = [ 674.06 674.72 ]
[ 1031 1032 ]
</pre></div>
<p>The matrices are stored in row major order, according to the C convention
for arrays.
</p>
<div class="example">
<pre class="verbatim">#include <stdio.h>
#include <gsl/gsl_blas.h>
int
main (void)
{
double a[] = { 0.11, 0.12, 0.13,
0.21, 0.22, 0.23 };
double b[] = { 1011, 1012,
1021, 1022,
1031, 1032 };
double c[] = { 0.00, 0.00,
0.00, 0.00 };
gsl_matrix_view A = gsl_matrix_view_array(a, 2, 3);
gsl_matrix_view B = gsl_matrix_view_array(b, 3, 2);
gsl_matrix_view C = gsl_matrix_view_array(c, 2, 2);
/* Compute C = A B */
gsl_blas_dgemm (CblasNoTrans, CblasNoTrans,
1.0, &A.matrix, &B.matrix,
0.0, &C.matrix);
printf ("[ %g, %g\n", c[0], c[1]);
printf (" %g, %g ]\n", c[2], c[3]);
return 0;
}
</pre></div>
<p>Here is the output from the program,
</p>
<div class="example">
<pre class="example">$ ./a.out
</pre><pre class="verbatim">[ 367.76, 368.12
674.06, 674.72 ]
</pre></div>
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