```/* nag_lapackeig_zhbevd (f08hqc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/

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

int main(void)
{
/* Scalars */
Integer i, j, k, kd, n, pdab, pdz, w_len;
Integer exit_status = 0;
NagError fail;
Nag_JobType job;
Nag_UploType uplo;
Nag_OrderType order;
/* Arrays */
char nag_enum_arg[40];
Complex *ab = 0, *z = 0;
double *w = 0;

#ifdef NAG_COLUMN_MAJOR
#define AB_UPPER(I, J) ab[(J - 1) * pdab + k + I - J - 1]
#define AB_LOWER(I, J) ab[(J - 1) * pdab + I - J]
#define Z(I, J) z[(J - 1) * pdz + I - 1]
order = Nag_ColMajor;
#else
#define AB_UPPER(I, J) ab[(I - 1) * pdab + J - I]
#define AB_LOWER(I, J) ab[(I - 1) * pdab + k + J - I - 1]
#define Z(I, J) z[(I - 1) * pdz + J - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_lapackeig_zhbevd (f08hqc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &kd);
pdab = kd + 1;
pdz = n;
w_len = n;

/* Allocate memory */
if (!(ab = NAG_ALLOC(pdab * n, Complex)) ||
!(w = NAG_ALLOC(w_len, double)) || !(z = NAG_ALLOC(n * n, Complex)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Read whether Upper or Lower part of A is stored */
scanf("%39s%*[^\n] ", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
uplo = (Nag_UploType) nag_enum_name_to_value(nag_enum_arg);
/* Read A from data file */
k = kd + 1;
if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= MIN(i + kd, n); ++j) {
scanf(" ( %lf , %lf )", &AB_UPPER(i, j).re, &AB_UPPER(i, j).im);
}
}
scanf("%*[^\n] ");
}
else {
for (i = 1; i <= n; ++i) {
for (j = MAX(1, i - kd); j <= i; ++j) {
scanf(" ( %lf , %lf )", &AB_LOWER(i, j).re, &AB_LOWER(i, j).im);
}
}
scanf("%*[^\n] ");
}
/* Read type of job to be performed */
scanf("%39s%*[^\n] ", nag_enum_arg);
job = (Nag_JobType) nag_enum_name_to_value(nag_enum_arg);
/* Calculate all the eigenvalues and eigenvectors of A */
/* nag_lapackeig_zhbevd (f08hqc).
* All eigenvalues and optionally all eigenvectors of
* complex Hermitian band matrix (divide-and-conquer)
*/
nag_lapackeig_zhbevd(order, job, uplo, n, kd, ab, pdab, w, z, pdz, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapackeig_zhbevd (f08hqc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Normalize the eigenvectors */
for (j = 1; j <= n; j++) {
for (i = n; i >= 1; i--) {
Z(i, j) = nag_complex_divide(Z(i, j), Z(1, j));
}
}
/* Print eigenvalues and eigenvectors */
printf(" Eigenvalues\n");
for (i = 0; i < n; ++i)
printf("   %5" NAG_IFMT "     %8.4f\n", i + 1, w[i]);
printf("\n");
/* nag_file_print_matrix_complex_gen_comp (x04dbc).
* Print complex general matrix (comprehensive)
*/
fflush(stdout);
nag_file_print_matrix_complex_gen_comp(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
n, z, pdz, Nag_AboveForm, "%7.4f",
"Eigenvectors", Nag_IntegerLabels, 0,
Nag_IntegerLabels, 0, 80, 0, 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_complex_gen_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(ab);
NAG_FREE(w);
NAG_FREE(z);
return exit_status;
}
```