```/* nag_dgtcon (f07cgc) Example Program.
*
* NAGPRODCODE Version.
*
* Copyright 2016 Numerical Algorithms Group.
*
* Mark 26, 2016.
*
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf07.h>
#include <nagx02.h>

int main(void)
{

/* Scalars */
double anorm, rcond;
Integer exit_status = 0, i, n;

/* Arrays */
double *d = 0, *dl = 0, *du = 0, *du2 = 0;
Integer *ipiv = 0;

/* Nag Types */
NagError fail;

INIT_FAIL(fail);

printf("nag_dgtcon (f07cgc) 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)) ||
!(dl = NAG_ALLOC(n - 1, double)) ||
!(du = NAG_ALLOC(n - 1, double)) ||
!(du2 = NAG_ALLOC(n - 2, double)) || !(ipiv = NAG_ALLOC(n, Integer)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

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

/* Compute the 1-norm of A */
if (n == 1) {
anorm = ABS(d[0]);
}
else {
anorm = MAX(ABS(d[0]) + ABS(dl[0]), ABS(d[n - 1]) + ABS(du[n - 2]));
for (i = 1; i < n - 1; ++i)
anorm = MAX(anorm, ABS(d[i]) + ABS(dl[i]) + ABS(du[i - 1]));
}

/* Factorize the tridiagonal matrix A using nag_dgttrf (f07cdc). */
nag_dgttrf(n, dl, d, du, du2, ipiv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_dgttrf (f07cdc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Estimate the condition number of A using nag_dgtcon (f07cgc). */
nag_dgtcon(Nag_OneNorm, n, dl, d, du, du2, ipiv, anorm, &rcond, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_dgtcon (f07cgc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the estimated condition number if A non-singular */
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(dl);
NAG_FREE(du);
NAG_FREE(du2);
NAG_FREE(ipiv);

return exit_status;
}
```