NAG Library Manual, Mark 27.2
```/* nag_lapacklin_zgbtrf (f07brc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

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

int main(void) {
/* Scalars */
Integer i, ipiv_len, j, kl, ku, m, n, pdab;
Integer exit_status = 0;
NagError fail;
Nag_OrderType order;

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

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

INIT_FAIL(fail);

printf("nag_lapacklin_zgbtrf (f07brc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &m, &n,
&kl, &ku);
ipiv_len = MIN(m, n);
pdab = 2 * kl + ku + 1;

/* Allocate memory */
if (!(ab = NAG_ALLOC((2 * kl + ku + 1) * n, Complex)) ||
!(ipiv = NAG_ALLOC(ipiv_len, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read A from data file */
for (i = 1; i <= m; ++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] ");

/* Factorize A */
/* nag_lapacklin_zgbtrf (f07brc).
* LU factorization of complex m by n band matrix
*/
nag_lapacklin_zgbtrf(order, m, n, kl, ku, ab, pdab, ipiv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_zgbtrf (f07brc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Print details of factorization */
/* nag_file_print_matrix_complex_band_comp (x04dfc).
* Print complex packed banded matrix (comprehensive)
*/
fflush(stdout);
nag_file_print_matrix_complex_band_comp(
order, m, 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("\nipiv\n");
for (i = 1; i <= MIN(m, n); ++i)
printf("%3" NAG_IFMT "%s", ipiv[i - 1],
i % 7 == 0 ? "\n" : "               ");
printf("\n");
END:
NAG_FREE(ab);
NAG_FREE(ipiv);
return exit_status;
}
```