```/* nag_herm_posdef_band_lin_solve (f04cfc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

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

int main(void)
{
double errbnd, rcond;
Integer exit_status, i, j, kd, n, nrhs, pdab, pdb;

/* Arrays */
char nag_enum_arg;
char *clabs = 0, *rlabs = 0;
Complex *ab = 0, *b = 0;

/* Nag types */
NagError fail;
Nag_OrderType order;
Nag_UploType uplo;

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

exit_status = 0;
INIT_FAIL(fail);

printf("nag_herm_posdef_band_lin_solve (f04cfc)"
" Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &kd, &nrhs);
if (n > 0 && kd > 0 && nrhs > 0) {
/* Allocate memory */
if (!(clabs = NAG_ALLOC(2, char)) ||
!(rlabs = NAG_ALLOC(2, char)) ||
!(ab = NAG_ALLOC((kd + 1) * n, Complex)) ||
!(b = NAG_ALLOC(n * nrhs, Complex)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
pdab = kd + 1;
#ifdef NAG_COLUMN_MAJOR
pdb = n;
#else
pdb = nrhs;
#endif
}
else {
printf("%s\n", "One or more of n, kd and nrhs is too small");
exit_status = 1;
return exit_status;
}

/* Read uplo storage name for the matrix A and convert to value. */
scanf("%19s%*[^\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 the upper or lower triangular part of the band matrix A */
/* from data file */

if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= MIN(n, i + kd); ++j) {
scanf(" ( %lf , %lf )", &AB_U(i, j).re, &AB_U(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_L(i, j).re, &AB_L(i, j).im);
}
scanf("%*[^\n] ");
}
}

/* Read B from data file */
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_herm_posdef_band_lin_solve (f04cfc).
* Computes the solution and error-bound to a complex
* Hermitian positive-definite banded system of linear
* equations
*/
nag_herm_posdef_band_lin_solve(order, uplo, n, kd, nrhs, ab, pdab, 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");
printf("%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_POS_DEF) {
/* The matrix A is not positive definite to working precision */
printf("%s%3" NAG_IFMT "%s\n\n", "The leading minor of order ",
fail.errnum, " is not positive definite");
}
else {
printf("Error from nag_herm_posdef_band_lin_solve (f04cfc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(clabs);
NAG_FREE(rlabs);
NAG_FREE(ab);
NAG_FREE(b);

return exit_status;
}

#undef AB
#undef B
```