```/* nag_matop_real_gen_matrix_actexp (f01gac) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/

#include <math.h>
#include <nag.h>

int main(void)
{

/* Scalars */
Integer exit_status = 0;
Integer i, j, m, n, lda, ldb;
double t;

/* Arrays */
double *a = 0;
double *b = 0;

/* Nag Types */
Nag_OrderType order;
NagError fail;

INIT_FAIL(fail);

#define A(I, J) a[(J-1)*lda + I-1]
#define B(I, J) b[(J-1)*ldb + I-1]

order = Nag_ColMajor;

/* Output preamble */
printf("nag_matop_real_gen_matrix_actexp (f01gac) ");
printf("Example Program Results\n\n");
fflush(stdout);

/* Skip heading in data file */
scanf("%*[^\n]");

/* Read in the problem size and the value of the parameter t */
scanf("%" NAG_IFMT " %" NAG_IFMT " %lf%*[^\n]", &n, &m, &t);

lda = n;
ldb = n;

if (!(a = NAG_ALLOC(n * n, double)) || !(b = NAG_ALLOC(n * m, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read in the matrix a from data file */
for (i = 1; i <= n; i++)
for (j = 1; j <= n; j++)
scanf("%lf", &A(i, j));
scanf("%*[^\n]");

/* Read in the matrix b from data file */
for (i = 1; i <= n; i++)
for (j = 1; j <= m; j++)
scanf("%lf", &B(i, j));
scanf("%*[^\n]");

/* Find exp(tA) B using
* nag_matop_real_gen_matrix_actexp (f01gac)
* Action of the the exponential of a real matrix on a real matrix
*/
nag_matop_real_gen_matrix_actexp(n, m, a, lda, b, ldb, t, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_matop_real_gen_matrix_actexp (f01gac)\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print solution using
* nag_file_print_matrix_real_gen (x04cac)
* Print real general matrix (easy-to-use)
*/
nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, m,
b, ldb, "exp(tA) B", NULL, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac)\n%s\n", fail.message);
exit_status = 2;
goto END;
}

END:
NAG_FREE(a);
NAG_FREE(b);
return exit_status;
}
```