NAG Library Manual, Mark 28.6
```/* nag_lapacklin_dptcon (f07jgc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.6, 2022.
*
* UNFINISHED - replace commented out climp calls
*/
#include <nag.h>
#include <stdio.h>

int main(void) {
/* Scalars */
double anorm, rcond;
Integer exit_status = 0, i, n;

/* Arrays */
double *d = 0, *e = 0;

/* Nag Types */
NagError fail;

INIT_FAIL(fail);

printf("nag_lapacklin_dptcon (f07jgc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
if (n < 0) {
printf("Invalid n\n");
exit_status = 1;
goto END;
}
/* Allocate memory */
if (!(d = NAG_ALLOC(n, double)) || !(e = NAG_ALLOC(n - 1, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read the lower bidiagonal part of the tridiagonal matrix A from */
/* data file */
for (i = 0; i < n; ++i)
scanf("%lf", &d[i]);
scanf("%*[^\n]");
for (i = 0; i < n - 1; ++i)
scanf("%lf", &e[i]);
scanf("%*[^\n]");

/* Compute the 1-norm of A */
anorm = MAX(ABS(d[0]) + ABS(e[0]), ABS(e[n - 2]) + ABS(d[n - 1]));
for (i = 1; i < n - 1; ++i)
anorm = MAX(anorm, ABS(d[i]) + ABS(e[i]) + ABS(e[i - 1]));

/* Factorize the tridiagonal matrix A using nag_lapacklin_dgbsv (f07bac). */
nag_lapacklin_dpttrf(n, d, e, &fail);

if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgbsv (f07bac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Estimate the condition number of A using nag_lapacklin_dptcon (f07jgc). */
nag_lapacklin_dptcon(n, d, e, anorm, &rcond, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dptcon (f07jgc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the estimated condition number */
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. RCOND = %11.2e\n\n", rcond);

END:
NAG_FREE(d);
NAG_FREE(e);

return exit_status;
}
```