NAG Library Manual, Mark 27.2
Interfaces:  FL   CL   CPP   AD
```/* nag_lapacklin_dtbcon (f07vgc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

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

int main(void) {
/* Scalars */
Integer i, j, k, kd, n, pdab;
Integer exit_status = 0;
double rcond;
NagError fail;
Nag_UploType uplo;
Nag_OrderType order;
/* Arrays */
char nag_enum_arg[40];
double *ab = 0;

#ifdef NAG_COLUMN_MAJOR
#define AB_UPPER(I, J) ab[(J - 1) * pdab + k + I - J - 1]
#define AB_LOWER(I, J) ab[(J - 1) * pdab + 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 + k + J - I - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_lapacklin_dtbcon (f07vgc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &kd);
pdab = kd + 1;

/* Allocate memory */
if (!(ab = NAG_ALLOC((kd + 1) * n, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read A from data file */
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);

k = kd + 1;
if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= MIN(i + kd, n); ++j)
scanf("%lf", &AB_UPPER(i, j));
}
scanf("%*[^\n] ");
} else {
for (i = 1; i <= n; ++i) {
for (j = MAX(1, i - kd); j <= i; ++j)
scanf("%lf", &AB_LOWER(i, j));
}
scanf("%*[^\n] ");
}
/* Estimate condition number */
/* nag_lapacklin_dtbcon (f07vgc).
* Estimate condition number of real band triangular matrix
*/
nag_lapacklin_dtbcon(order, Nag_OneNorm, uplo, Nag_NonUnitDiag, n, kd, ab,
pdab, &rcond, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dtbcon (f07vgc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* nag_machine_precision (x02ajc).
* The machine precision
*/
if (rcond >= nag_machine_precision) {
printf("Estimate of condition number =%11.2e\n\n", 1.0 / rcond);
} else
printf("A is singular to working precision\n");
END:
NAG_FREE(ab);
return exit_status;
}
```