```/* nag_complex_band_lin_solve (f04cbc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 8, 2004.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf04.h>
#include <nagx04.h>

int main(void)
{
/* Scalars */
double        errbnd, rcond;
Integer       exit_status, i, j, kl, ku, n, nrhs, pdab, pdb;

/* Arrays */
char          *clabs = 0, *rlabs = 0;
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

exit_status = 0;
INIT_FAIL(fail);

printf("nag_complex_band_lin_solve (f04cbc)"
" Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%ld%ld%ld%ld%*[^\n] ",
&n, &kl, &ku, &nrhs);
if (n > 0 && kl > 0 && ku > 0 && nrhs > 0)
{
/* Allocate memory */
if (!(clabs = NAG_ALLOC(2, char)) ||
!(rlabs = NAG_ALLOC(2, char)) ||
!(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
}
else
{
printf("%s\n", "One or more of NMAX, KLMAX, KUMAX or NRHSMX is"
" too small");
exit_status = 1;
return exit_status;
}

/* Read A and 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 */
/* nag_complex_band_lin_solve (f04cbc).
* Computes the solution and error-bound to a complex banded
* system of linear equations
*/
nag_complex_band_lin_solve(order, n, kl, ku, nrhs, ab, pdab, ipiv, b,
pdb, &rcond, &errbnd, &fail);
if (fail.code == NE_NOERROR)
{
/* Print solution, estimate of condition number and approximate */
/* error bound */
/* nag_gen_complx_mat_print_comp (x04dbc).
* Print complex general matrix (comprehensive)
*/
fflush(stdout);
nag_gen_complx_mat_print_comp(order, Nag_GeneralMatrix,
Nag_NonUnitDiag, n, nrhs, b, pdb,
Nag_BracketForm, "%7.4f",
"Solution", Nag_IntegerLabels, 0,
Nag_IntegerLabels, 0, 80, 0, 0,
&fail);
if (fail.code != NE_NOERROR)
{
printf(
"Error from nag_gen_complx_mat_print_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("\n%s\n%4s%10.1e\n\n", "Estimate of condition number", "",
1.0/rcond);
printf("\n%s\n%4s%10.1e\n\n",
"Estimate of error bound for computed solutions", "",
errbnd);
}
else if (fail.code == NE_RCOND)
{
/* Matrix A is numerically singular.  Print estimate of */
/* reciprocal of condition number and solution */
printf("\n%s\n%4s%10.1e\n\n\n",
"Estimate of reciprocal of condition number", "", rcond);
/* nag_gen_complx_mat_print_comp (x04dbc), see above. */
fflush(stdout);
nag_gen_complx_mat_print_comp(order, Nag_GeneralMatrix,
Nag_NonUnitDiag, n, nrhs, b, pdb,
Nag_BracketForm, "%7.4f",
"Solution", Nag_IntegerLabels, 0,
Nag_IntegerLabels, 0, 80, 0, 0,
&fail);
if (fail.code != NE_NOERROR)
{
printf(
"Error from nag_gen_complx_mat_print_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
}
else if (fail.code == NE_SINGULAR)
{
/* The upper triangular matrix U is exactly singular.  Print */
/* details of factorization */

printf("\n");
/* nag_band_complx_mat_print_comp (x04dfc).
* Print complex packed banded matrix (comprehensive)
*/
fflush(stdout);
nag_band_complx_mat_print_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_band_complx_mat_print_comp (x04dfc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print pivot indices */

printf("\n%s\n", "Pivot indices");
for (i = 1; i <= n; ++i)
{
printf("%11ld%s", ipiv[i - 1],
i%7 == 0 || i == n?"\n":" ");
}
printf("\n");
}
else
{
printf("Error from nag_complex_band_lin_solve (f04cbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(clabs);
NAG_FREE(rlabs);
NAG_FREE(ab);
NAG_FREE(b);
NAG_FREE(ipiv);

return exit_status;
}
```