NAG Library Manual, Mark 28.5
```/* nag_sparse_direct_real_gen_matmul (f11mkc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.5, 2022.
*/

#include <nag.h>
#include <stdio.h>

/* Table of constant values */

static double alpha = 1.;
static double beta = 0.;

int main(void) {
Integer exit_status = 0, i, j, m, n, nnz;
double *a = 0, *b = 0, *c = 0;
Integer *icolzp = 0, *irowix = 0;
/* Nag types */
NagError fail;
Nag_OrderType order = Nag_ColMajor;
Nag_MatrixType matrix = Nag_GeneralMatrix;
Nag_DiagType diag = Nag_NonUnitDiag;
Nag_TransType trans;

INIT_FAIL(fail);

printf(
"nag_sparse_direct_real_gen_matmul (f11mkc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n] ");
/* Read order of matrix */
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &m);
/* Read the matrix A */
if (!(icolzp = NAG_ALLOC(n + 1, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
for (i = 0; i < n + 1; ++i)
scanf("%" NAG_IFMT "%*[^\n] ", &icolzp[i]);
nnz = icolzp[n] - 1;
/* Allocate memory */
if (!(irowix = NAG_ALLOC(nnz, Integer)) || !(a = NAG_ALLOC(nnz, double)) ||
!(b = NAG_ALLOC(n * m, double)) || !(c = NAG_ALLOC(n * m, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
for (i = 0; i < nnz; ++i)
scanf("%lf%" NAG_IFMT "%*[^\n] ", &a[i], &irowix[i]);
/* Read the matrix B */
for (j = 0; j < m; ++j) {
for (i = 0; i < n; ++i) {
scanf("%lf", &b[j * n + i]);
c[j * n + i] = 0.0;
}
scanf("%*[^\n] ");
}
/* Calculate matrix-matrix product */
trans = Nag_NoTrans;
/* nag_sparse_direct_real_gen_matmul (f11mkc).
* Real sparse nonsymmetric matrix matrix multiply,
* compressed column storage
*/
nag_sparse_direct_real_gen_matmul(order, trans, n, m, alpha, icolzp, irowix,
a, b, n, beta, c, n, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_direct_real_gen_matmul (f11mkc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Output results */
printf("\n");
/* nag_file_print_matrix_real_gen (x04cac).
* Print real general matrix (easy-to-use)
*/
fflush(stdout);
nag_file_print_matrix_real_gen(order, matrix, diag, n, m, c, n,
"Matrix-vector product", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Calculate transposed matrix-matrix product */
trans = Nag_Trans;
/* nag_sparse_direct_real_gen_matmul (f11mkc), see above. */
nag_sparse_direct_real_gen_matmul(order, trans, n, m, alpha, icolzp, irowix,
a, b, n, beta, c, n, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_direct_real_gen_matmul (f11mkc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Output results */
printf("\n");
/* nag_file_print_matrix_real_gen (x04cac), see above. */
fflush(stdout);
nag_file_print_matrix_real_gen(order, matrix, diag, n, m, c, n,
"Transposed matrix-vector product", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(a);
NAG_FREE(b);
NAG_FREE(c);
NAG_FREE(icolzp);
NAG_FREE(irowix);

return exit_status;
}
```