BLAS Examples - GNU Scientific Library -- Reference Manual
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### 13.2 Examples

The following program computes the product of two matrices using the Level-3 blas function dgemm,

         [ 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 ]

The matrices are stored in row major order, according to the C convention for arrays.

         #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;
         }

Here is the output from the program,

         $ ./a.out
         [ 367.76, 368.12
           674.06, 674.72 ]

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