```/* nag_zhbgst (f08usc) Example Program.
*
* NAGPRODCODE Version.
*
* Copyright 2016 Numerical Algorithms Group.
*
* Mark 26, 2016.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf08.h>

int main(void)
{
/* Scalars */
Integer i, j, k1, k2, ka, kb, n, pdab, pdbb, pdx, d_len, e_len;
Integer exit_status = 0;
NagError fail;
Nag_UploType uplo;
Nag_OrderType order;
/* Arrays */
char nag_enum_arg[40];
Complex *ab = 0, *bb = 0, *x = 0;
double *d = 0, *e = 0;

#ifdef NAG_COLUMN_MAJOR
#define AB_UPPER(I, J) ab[(J-1)*pdab + k1 + I - J - 1]
#define AB_LOWER(I, J) ab[(J-1)*pdab + I - J]
#define BB_UPPER(I, J) bb[(J-1)*pdbb + k2 + I - J - 1]
#define BB_LOWER(I, J) bb[(J-1)*pdbb + I - J]
order = Nag_ColMajor;
#else
#define AB_UPPER(I, J) ab[(I-1)*pdab + J - I]
#define AB_LOWER(I, J) ab[(I-1)*pdab + k1 + J - I - 1]
#define BB_UPPER(I, J) bb[(I-1)*pdbb + J - I]
#define BB_LOWER(I, J) bb[(I-1)*pdbb + k2 + J - I - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_zhbgst (f08usc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &ka, &kb);
pdab = ka + 1;
pdbb = kb + 1;
pdx = n;
d_len = n;
e_len = n - 1;

/* Allocate memory */
if (!(ab = NAG_ALLOC(pdab * n, Complex)) ||
!(bb = NAG_ALLOC(pdbb * n, Complex)) ||
!(d = NAG_ALLOC(d_len, double)) ||
!(e = NAG_ALLOC(e_len, double)) || !(x = 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 and B from data file */
k1 = ka + 1;
k2 = kb + 1;
if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= MIN(i + ka, 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 - ka); j <= i; ++j) {
scanf(" ( %lf , %lf ) ", &AB_LOWER(i, j).re, &AB_LOWER(i, j).im);
}
}
scanf("%*[^\n] ");
}
if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= MIN(i + kb, n); ++j) {
scanf(" ( %lf, %lf ) ", &BB_UPPER(i, j).re, &BB_UPPER(i, j).im);
}
}
scanf("%*[^\n] ");
}
else {
for (i = 1; i <= n; ++i) {
for (j = MAX(1, i - kb); j <= i; ++j) {
scanf(" ( %lf, %lf ) ", &BB_LOWER(i, j).re, &BB_LOWER(i, j).im);
}
}
scanf("%*[^\n] ");
}
/* Compute the split Cholesky factorization of B */
/* nag_zpbstf (f08utc).
* Computes a split Cholesky factorization of complex
* Hermitian positive-definite band matrix A
*/
nag_zpbstf(order, uplo, n, kb, bb, pdbb, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zpbstf (f08utc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Reduce the problem to standard form C*y = lambda*y, */
/* storing the result in A */
/* nag_zhbgst (f08usc).
* Reduction of complex Hermitian-definite banded
* generalized eigenproblem Ax = lambda Bx to standard form
* Cy = lambda y, such that C has the same bandwidth as A
*/
nag_zhbgst(order, Nag_DoNotForm, uplo, n, ka, kb, ab, pdab, bb, pdbb,
x, pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zhbgst (f08usc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Reduce C to tridiagonal form T = (Q^T)*C*Q */
/* nag_zhbtrd (f08hsc).
* Unitary reduction of complex Hermitian band matrix to
* real symmetric tridiagonal form
*/
nag_zhbtrd(order, Nag_DoNotForm, uplo, n, ka, ab, pdab, d, e,
x, pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zhbtrd (f08hsc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Calculate the eigenvalues of T (same as C) */
/* nag_dsterf (f08jfc).
* All eigenvalues of real symmetric tridiagonal matrix,
* root-free variant of QL or QR
*/
nag_dsterf(n, d, e, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_dsterf (f08jfc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Print eigenvalues */
printf(" Eigenvalues\n");
for (i = 0; i < n; ++i)
printf(" %8.4lf", d[i]);
printf("\n");
END:
NAG_FREE(ab);
NAG_FREE(bb);
NAG_FREE(d);
NAG_FREE(e);
NAG_FREE(x);
return exit_status;
}
```