NAG Library Manual, Mark 28.6
```/* nag_lapacklin_zgbsv (f07bnc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.6, 2022.
*/

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

int main(void) {

/* Scalars */
Integer exit_status = 0, i, j, kl, ku, n, nrhs, pdab, pdb;

/* Arrays */
Complex *ab = 0, *b = 0;
Integer *ipiv = 0;

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

#ifdef NAG_COLUMN_MAJOR
#define AB(I, J) ab[(J - 1) * pdab + kl + ku + I - J]
#define B(I, J) b[(J - 1) * pdb + I - 1]
order = Nag_ColMajor;
#else
#define AB(I, J) ab[(I - 1) * pdab + kl + J - I]
#define B(I, J) b[(I - 1) * pdb + J - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_lapacklin_zgbsv (f07bnc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &n, &kl, &ku);
scanf("%" NAG_IFMT "%*[^\n]", &nrhs);
if (n < 0 || kl < 0 || ku < 0 || nrhs < 0) {
printf("Invalid n, kl, ku or nrhs\n");
exit_status = 1;
goto END;
}
/* Allocate memory */
if (!(ab = NAG_ALLOC((2 * kl + ku + 1) * n, Complex)) ||
!(b = NAG_ALLOC(n * nrhs, Complex)) || !(ipiv = NAG_ALLOC(n, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

pdab = 2 * kl + ku + 1;
#ifdef NAG_COLUMN_MAJOR
pdb = n;
#else
pdb = nrhs;
#endif
/* Read the band matrix A and the right hand side b from data file */
for (i = 1; i <= n; ++i)
for (j = MAX(i - kl, 1); j <= MIN(i + ku, n); ++j)
scanf(" ( %lf , %lf )", &AB(i, j).re, &AB(i, j).im);
scanf("%*[^\n]");
for (i = 1; i <= n; ++i)
for (j = 1; j <= nrhs; ++j)
scanf(" ( %lf , %lf )", &B(i, j).re, &B(i, j).im);
scanf("%*[^\n]");

/* Solve the equations Ax = b for x using nag_lapacklin_zgbsv (f07bnc). */
nag_lapacklin_zgbsv(order, n, kl, ku, nrhs, ab, pdab, ipiv, b, pdb, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_zgbsv (f07bnc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("Solution\n");
for (i = 1; i <= n; ++i) {
for (j = 1; j <= nrhs; ++j)
printf("(%7.4f, %7.4f)%s", B(i, j).re, B(i, j).im,
j % 4 == 0 ? "\n" : " ");
printf("\n");
}
printf("\n");

/* Print details of the factorization using
* nag_file_print_matrix_complex_band_comp (x04dfc).
*/
fflush(stdout);
nag_file_print_matrix_complex_band_comp(
order, n, n, kl, kl + ku, ab, pdab, Nag_BracketForm, "%7.4f",
"Details of factorization", Nag_IntegerLabels, 0, Nag_IntegerLabels, 0,
80, 0, 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_complex_band_comp (x04dfc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
/* Print pivot indices' */
printf("\nPivot indices\n");
for (i = 1; i <= n; ++i)
printf("%11" NAG_IFMT "", ipiv[i - 1]);
printf("\n");
END:
NAG_FREE(ab);
NAG_FREE(b);
NAG_FREE(ipiv);
return exit_status;
}

#undef AB
#undef B
```