/* nag_dgtcon (f07cgc) Example Program.
 *
 * Copyright 2004 Numerical Algorithms Group.
 *
 * Mark 23, 2011
 *
 */

#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("%ld%*[^\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:
  if (d) NAG_FREE(d);
  if (dl) NAG_FREE(dl);
  if (du) NAG_FREE(du);
  if (du2) NAG_FREE(du2);
  if (ipiv) NAG_FREE(ipiv);

  return exit_status;
}