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<title>GNU Scientific Library &ndash; Reference Manual: GSL CBLAS Examples</title>

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<a name="GSL-CBLAS-Examples"></a>
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<p>
Previous: <a href="Level-3-CBLAS-Functions.html#Level-3-CBLAS-Functions" accesskey="p" rel="previous">Level 3 CBLAS Functions</a>, Up: <a href="GSL-CBLAS-Library.html#GSL-CBLAS-Library" accesskey="u" rel="up">GSL CBLAS Library</a> &nbsp; [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Examples-34"></a>
<h3 class="section">D.4 Examples</h3>

<p>The following program computes the product of two matrices using the
Level-3 <small>BLAS</small> function <small>SGEMM</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 but could be stored in column
major order if the first argument of the call to <code>cblas_sgemm</code> was
changed to <code>CblasColMajor</code>.
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_cblas.h&gt;

int
main (void)
{
  int lda = 3;

  float A[] = { 0.11, 0.12, 0.13,
                0.21, 0.22, 0.23 };

  int ldb = 2;
  
  float B[] = { 1011, 1012,
                1021, 1022,
                1031, 1032 };

  int ldc = 2;

  float C[] = { 0.00, 0.00,
                0.00, 0.00 };

  /* Compute C = A B */

  cblas_sgemm (CblasRowMajor, 
               CblasNoTrans, CblasNoTrans, 2, 2, 3,
               1.0, A, lda, B, ldb, 0.0, C, ldc);

  printf (&quot;[ %g, %g\n&quot;, C[0], C[1]);
  printf (&quot;  %g, %g ]\n&quot;, C[2], C[3]);

  return 0;  
}
</pre></div>

<p>To compile the program use the following command line,
</p>
<div class="example">
<pre class="example">$ gcc -Wall demo.c -lgslcblas
</pre></div>

<p>There is no need to link with the main library <code>-lgsl</code> in this
case as the <small>CBLAS</small> library is an independent unit. 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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