```/* nag_eigen_real_gen_eigsys (f02ecc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*
*/

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

#define MMAX 3
#define A(I, J) a[(I) *tda + J]
#define V(I, J) v[(I) *tdv + J]
int main(void)
{

Complex *v = 0, *w = 0;
Integer exit_status = 0, i, j, m, mest, n, tda, tdv;
double *a = 0, wl, wu;

NagError fail;

INIT_FAIL(fail);

printf("nag_eigen_real_gen_eigsys (f02ecc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n]");
mest = MMAX;
scanf("%" NAG_IFMT "%lf%lf%*[^\n]", &n, &wl, &wu);

if (n >= 0) {
if (!(a = NAG_ALLOC(n * n, double)) ||
!(w = NAG_ALLOC(n, Complex)) || !(v = NAG_ALLOC(n * mest, Complex)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
tda = n;
tdv = mest;
}
else {
printf("Invalid n.\n");
exit_status = 1;
return exit_status;
}
/* Read a from data file */
for (i = 0; i < n; ++i)
for (j = 0; j < n; ++j)
scanf("%lf", &A(i, j));
scanf("%*[^\n]");

/* Compute selected eigenvalues and eigenvectors of A */

/* nag_eigen_real_gen_eigsys (f02ecc).
* Computes selected eigenvalues and eigenvectors of a real
* general matrix
*/
nag_eigen_real_gen_eigsys(Nag_Select_Modulus, n, a, tda, wl, wu, mest, &m, w,
v, tdv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_eigen_real_gen_eigsys (f02ecc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("\n\nEigenvalues\n");
for (i = 0; i < m; ++i)
printf("(%7.4f, %7.4f)  ", w[i].re, w[i].im);
printf("\n");

printf(" Eigenvectors\n    ");
for (i = 1; i <= m; i++)
printf("%15" NAG_IFMT "%s", i, i % m == 0 ? "\n" : "");
for (i = 0; i < n; i++) {
printf("%" NAG_IFMT "  ", i + 1);
for (j = 0; j < m; j++)
printf("(%8.4f, %8.4f)%s", V(i, j).re,
V(i, j).im, (j + 1) % m == 0 ? "\n" : "  ");
}
END:
NAG_FREE(a);
NAG_FREE(w);
NAG_FREE(v);
return exit_status;
}
```