/* nag_real_sym_posdef_tridiag_lin_solve (f04bgc) Example Program.
 *
 * Copyright 2004 Numerical Algorithms Group.
 *
 * Mark 8, 2004.
 */

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

int main(void)
{

  /* Scalars */
  double errbnd, rcond;
  Integer exit_status, i,  j, n, nrhs, pdb;

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

  /* Nag Types */
  NagError fail;
  Nag_OrderType order;

#ifdef NAG_COLUMN_MAJOR
#define B(I,J) b[(J-1)*pdb + I - 1]
  order = Nag_ColMajor;
#else
#define B(I,J) b[(I-1)*pdb + J - 1]
  order = Nag_RowMajor;
#endif
#define b_ref(a_1,a_2) b[(a_2)*8 + a_1 - 9]

  exit_status = 0;
  INIT_FAIL(fail);

  Vprintf("nag_real_sym_posdef_tridiag_lin_solve (f04bgc) Example Program"
          " Results\n\n");

  /* Skip heading in data file */
  Vscanf("%*[^\n] ");
  Vscanf("%ld%ld%*[^\n] ",   &n,  &nrhs);
  if (n>0 && nrhs>0)
    {
      /* Allocate memory */
      if ( !(b = NAG_ALLOC(n*nrhs, double)) ||
           !(d = NAG_ALLOC(n, double)) ||
           !(e = NAG_ALLOC(n-1, double)) )
        {
          Vprintf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
#ifdef NAG_COLUMN_MAJOR
      pdb = n;
#else
      pdb = nrhs;
#endif
    }
  else
    {
      Vprintf("%s\n",   "n and/or nrhs too small");
      exit_status = 1;
      return exit_status;
    }

  /* Read A from data file */
  for (i = 1; i<=n; ++i)
    {
      Vscanf("%lf", &d[i-1]);
    }
  Vscanf("%*[^\n] ");

  for (i = 1;i<=n-1; ++i)
    {
      Vscanf("%lf", &e[i-1]);
    }
  Vscanf("%*[^\n] ");

  /* Read B from data file */
  for (i=1; i<= n; ++i)
    {
      for (j=1; j<=nrhs; ++j)
        {
          Vscanf("%lf", &B(i,j));
        }
    }
  Vscanf("%*[^\n] ");

  /* Solve the equations AX = B for X */
  /* nag_real_sym_posdef_tridiag_lin_solve (f04bgc).
   * Computes the solution and error-bound to a real symmetric
   * positive-definite tridiagonal system of linear equations
   */
  nag_real_sym_posdef_tridiag_lin_solve(order, n, nrhs, d, e, b, pdb, &rcond,
                                        &errbnd, &fail);
  if (fail.code == NE_NOERROR)
    {

      /* Print solution, estimate of condition number and approximate */
      /* error bound */

      /* nag_gen_real_mat_print (x04cac).
       * Print real general matrix (easy-to-use)
       */
      nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag,  n,
                             nrhs, b, pdb, "Solution", 0, &fail);
      if (fail.code != NE_NOERROR)
        {
          Vprintf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
                  fail.message);
          exit_status = 1;
          goto END;
        }
      Vprintf("\n%s\n%6s%9.1e\n", "Estimate of condition number", "",
              1.0/rcond);
      Vprintf("\n\n");
      Vprintf("%s\n%6s", "Estimate of error bound for computed solutions", "");
      Vprintf("%9.1e\n\n", errbnd);
    }
  else if (fail.code == NE_RCOND)
    {

      /* Matrix A is numerically singular.  Print estimate of */
      /* reciprocal of condition number and solution */
      Vprintf("\n");
      Vprintf("%s\n%6s%9.1e\n", "Estimate of reciprocal of condition number",
              "",  rcond);
      Vprintf("\n\n");

      /* nag_gen_real_mat_print (x04cac), see above. */
      nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag,  n,
                             nrhs, b, pdb, "Solution", 0, &fail);
      if (fail.code != NE_NOERROR)
        {
          Vprintf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
                  fail.message);
          exit_status = 1;
          goto END;
        }
    }
  else if (fail.code == NE_POS_DEF)
    {
      Vprintf("%s%3ld%s\n\n", "The leading minor of order ",
              fail.errnum, " is not positive definite");
    }
 END:
  if (b) NAG_FREE(b);
  if (d) NAG_FREE(d);
  if (e) NAG_FREE(e);
  return exit_status;
}