NAG Library Manual, Mark 27.2
Interfaces:  FL   CL   CPP   AD
```/* nag_matop_real_gen_matrix_fun_num (f01elc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

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

#ifdef __cplusplus
extern "C" {
#endif
static void NAG_CALL f(Integer *iflag, Integer n, const Complex z[],
Complex fz[], Nag_Comm *comm);
#ifdef __cplusplus
}
#endif

int main(void) {
/* Scalars */
Integer exit_status = 0;
Integer i, iflag, j, n, pda;
double imnorm;

/* Arrays */
static double ruser[1] = {-1.0};
double *a = 0;

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

INIT_FAIL(fail);

#define A(I, J) a[(J - 1) * pda + I - 1]

order = Nag_ColMajor;

/* Output preamble */
printf("nag_matop_real_gen_matrix_fun_num (f01elc) ");
printf("Example Program Results\n\n");
fflush(stdout);

/* For communication with user-supplied functions: */
comm.user = ruser;

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

/* Read in the problem size */
scanf("%" NAG_IFMT "%*[^\n]", &n);

pda = n;
if (!(a = NAG_ALLOC(pda * n, 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]");
/* Find the matrix function using
* nag_matop_real_gen_matrix_fun_num (f01elc)
* Function of a real matrix
*/
nag_matop_real_gen_matrix_fun_num(n, a, pda, f, &comm, &iflag, &imnorm,
&fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_matop_real_gen_matrix_fun_num (f01elc)\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

if (fabs(imnorm) > pow(nag_machine_precision, 0.8)) {
printf("\nWARNING: the error estimate returned in imnorm is larger than"
" expected;\n");
printf("         the matrix solution printed below is suspect:\n");
printf("         imnorm = %13.4e.\n\n", imnorm);
}

/* Print solution using
* nag_file_print_matrix_real_gen (x04dac)
* Print real general matrix (easy-to-use)
*/
nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
n, a, pda, "f(A) = cos(2A)", NULL, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04dac)\n%s\n",
fail.message);
exit_status = 2;
goto END;
}

END:
NAG_FREE(a);
return exit_status;
}

static void NAG_CALL f(Integer *iflag, Integer n, const Complex z[],
Complex fz[], Nag_Comm *comm) {
/* Scalars */
Integer j;
#ifdef _OPENMP
#pragma omp master
#endif
if (comm->user[0] == -1.0) {
printf("(User-supplied callback f, first invocation.)\n");
fflush(stdout);
comm->user[0] = 0.0;
}
for (j = 0; j < n; j++) {
/* Complex representation of cos 2z */
fz[j].re = cos(2.0 * z[j].re) * cosh(2.0 * z[j].im);
fz[j].im = -sin(2.0 * z[j].re) * sinh(2.0 * z[j].im);
}
/* Set iflag nonzero to terminate execution for any reason. */
*iflag = 0;
}
```