/* 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(int argc, char *argv[])
{
  FILE          *fpin, *fpout;
  char          *outfile = 0;
  /* 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);

  /* Check for command-line IO options */
  fpin = nag_example_file_io(argc, argv, "-data", NULL);
  fpout = nag_example_file_io(argc, argv, "-results", NULL);
  (void) nag_example_file_io(argc, argv, "-nag_write", &outfile);

  fprintf(fpout, "nag_real_sym_posdef_tridiag_lin_solve (f04bgc) Example "
          "Program Results\n\n");

  /* Skip heading in data file */
  fscanf(fpin, "%*[^\n] ");
  fscanf(fpin, "%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)))
        {
          fprintf(fpout, "Allocation failure\n");
          exit_status = -1;
          goto END;
        }
#ifdef NAG_COLUMN_MAJOR
      pdb = n;
#else
      pdb = nrhs;
#endif
    }
  else
    {
      fprintf(fpout, "%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)
    {
      fscanf(fpin, "%lf", &d[i-1]);
    }
  fscanf(fpin, "%*[^\n] ");

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

  /* Read B from data file */
  for (i = 1; i <= n; ++i)
    {
      for (j = 1; j <= nrhs; ++j)
        {
          fscanf(fpin, "%lf", &B(i, j));
        }
    }
  fscanf(fpin, "%*[^\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)
       */
      if (outfile) fclose(fpout);
      nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                             nrhs, b, pdb, "Solution", outfile, &fail);
      if (outfile && !(fpout = fopen(outfile, "a")))
        {
          exit_status = 2;
          goto END;
        }
      if (fail.code != NE_NOERROR)
        {
          fprintf(fpout, "Error from nag_gen_real_mat_print (x04cac).\n%s\n",
                  fail.message);
          exit_status = 1;
          goto END;
        }
      fprintf(fpout, "\n%s\n%6s%10.1e\n", "Estimate of condition number", "",
              1.0/rcond);
      fprintf(fpout, "\n\n");
      fprintf(fpout, "%s\n%6s",
              "Estimate of error bound for computed solutions",
              "");
      fprintf(fpout, "%10.1e\n\n", errbnd);
    }
  else if (fail.code == NE_RCOND)
    {
      /* Matrix A is numerically singular.  Print estimate of */
      /* reciprocal of condition number and solution */
      fprintf(fpout, "\n");
      fprintf(fpout, "%s\n%6s%10.1e\n",
              "Estimate of reciprocal of condition number", "", rcond);
      fprintf(fpout, "\n\n");

      /* nag_gen_real_mat_print (x04cac), see above. */
      if (outfile) fclose(fpout);
      nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                             nrhs, b, pdb, "Solution", outfile, &fail);
      if (outfile && !(fpout = fopen(outfile, "a")))
        {
          exit_status = 2;
          goto END;
        }
      if (fail.code != NE_NOERROR)
        {
          fprintf(fpout, "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)
    {
      fprintf(fpout, "%s%3ld%s\n\n", "The leading minor of order ",
              fail.errnum, " is not positive definite");
    }
  else
    {
      fprintf(
        fpout,
        "Error from nag_real_sym_posdef_tridiag_lin_solve (f04bgc).\n%s\n",
        fail.message);
      exit_status = 1;
      goto END;
    }
 END:
  if (fpin != stdin) fclose(fpin);
  if (fpout != stdout) fclose(fpout);
  if (b) NAG_FREE(b);
  if (d) NAG_FREE(d);
  if (e) NAG_FREE(e);
  return exit_status;
}