NAG Library Manual, Mark 28.4
```/* nag_lapackeig_dgeev (f08nac) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.4, 2022.
*/

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

int main(void) {

/* Scalars */
Integer i, j, n, pda, pdvr;
Integer exit_status = 0;

/* Arrays */
double *a = 0, *vr = 0, *wi = 0, *wr = 0;
double dummy[1];

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

#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J - 1) * pda + I - 1]
#define VR(I, J) vr[(J)*pdvr + I]
order = Nag_ColMajor;
#else
#define A(I, J) a[(I - 1) * pda + J - 1]
#define VR(I, J) vr[(I)*pdvr + J]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_lapackeig_dgeev (f08nac) Example Program Results\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
if (n < 0) {
printf("Invalid n\n");
exit_status = 1;
goto END;
}

pda = n;
pdvr = n;
/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, double)) || !(vr = NAG_ALLOC(n * n, double)) ||
!(wi = NAG_ALLOC(n, double)) || !(wr = NAG_ALLOC(n, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read 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]");

/* Compute the eigenvalues and right eigenvectors only of A
* using nag_lapackeig_dgeev (f08nac).
*/
nag_lapackeig_dgeev(order, Nag_NotLeftVecs, Nag_RightVecs, n, a, pda, wr, wi,
dummy, 1, vr, pdvr, &fail);

if (fail.code != NE_NOERROR) {
printf("Error from nag_lapackeig_dgeev (f08nac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print eigenvalues and right eigenvectors. */
for (j = 0; j < n; ++j) {
printf("\nEigenvalue %3" NAG_IFMT " = ", j + 1);
if (wi[j] == 0.0)
printf("%13.4e\n", wr[j]);
else
printf(" (%13.4e, %13.4e)\n", wr[j], wi[j]);

printf("\nEigenvector %2" NAG_IFMT "\n", j + 1);
if (wi[j] == 0.0)
for (i = 0; i < n; ++i)
printf("%17s%13.4e\n", "", VR(i, j));
else if (wi[j] > 0.0)
for (i = 0; i < n; ++i)
printf("%18s(%13.4e, %13.4e)\n", "", VR(i, j), VR(i, j + 1));
else
for (i = 0; i < n; ++i)
printf("%18s(%13.4e, %13.4e)\n", "", VR(i, j - 1), -VR(i, j));
printf("\n");
}

END:
NAG_FREE(a);
NAG_FREE(vr);
NAG_FREE(wi);
NAG_FREE(wr);

return exit_status;
}

#undef A
#undef VR
```