/* nag_dsygst (f08sec) Example Program.
 *
 * Copyright 2001 Numerical Algorithms Group.
 *
 * Mark 7, 2001.
 */

#include <stdio.h>
#include <nag.h>
#include <nagx04.h>
#include <nag_stdlib.h>
#include <nagf07.h>
#include <nagf08.h>

int main(int argc, char *argv[])
{
  FILE          *fpin, *fpout;
  /* Scalars */
  Integer       i, j, n, pda, pdb, d_len, e_len, tau_len;
  Integer       exit_status = 0;
  NagError      fail;
  Nag_UploType  uplo;
  Nag_OrderType order;
  /* Arrays */
  char          nag_enum_arg[40];
  double        *a = 0, *b = 0, *d = 0, *e = 0, *tau = 0;

#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J-1)*pda + I - 1]
#define B(I, J) b[(J-1)*pdb + I - 1]
  order = Nag_ColMajor;
#else
#define A(I, J) a[(I-1)*pda + J - 1]
#define B(I, J) b[(I-1)*pdb + J - 1]
  order = Nag_RowMajor;
#endif

  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);
  fprintf(fpout, "nag_dsygst (f08sec) Example Program Results\n\n");

  /* Skip heading in data file */
  fscanf(fpin, "%*[^\n] ");
  fscanf(fpin, "%ld%*[^\n] ", &n);
#ifdef NAG_COLUMN_MAJOR
  pda = n;
  pdb = n;
#else
  pda = n;
  pdb = n;
#endif
  d_len = n;
  e_len = n-1;
  tau_len = n-1;

  /* Allocate memory */
  if (!(a = NAG_ALLOC(n * n, double)) ||
      !(b = NAG_ALLOC(n * n, double)) ||
      !(d = NAG_ALLOC(d_len, double)) ||
      !(e = NAG_ALLOC(e_len, double)) ||
      !(tau = NAG_ALLOC(tau_len, double)))
    {
      fprintf(fpout, "Allocation failure\n");
      exit_status = -1;
      goto END;
    }
  /* Read A and B from data file */
  fscanf(fpin, "%s%*[^\n] ", nag_enum_arg);
  /* nag_enum_name_to_value(x04nac).
   * Converts NAG enum member name to value
   */
  uplo = (Nag_UploType) nag_enum_name_to_value(nag_enum_arg);
  if (uplo == Nag_Upper)
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = i; j <= n; ++j)
            fscanf(fpin, "%lf", &A(i, j));
        }
      fscanf(fpin, "%*[^\n] ");
      for (i = 1; i <= n; ++i)
        {
          for (j = i; j <= n; ++j)
            fscanf(fpin, "%lf", &B(i, j));
        }
      fscanf(fpin, "%*[^\n] ");
    }
  else
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = 1; j <= i; ++j)
            fscanf(fpin, "%lf", &A(i, j));
        }
      fscanf(fpin, "%*[^\n] ");
      for (i = 1; i <= n; ++i)
        {
          for (j = 1; j <= i; ++j)
            fscanf(fpin, "%lf", &B(i, j));
        }
      fscanf(fpin, "%*[^\n] ");
    }

  /* Compute the Cholesky factorization of B */
  /* nag_dpotrf (f07fdc).
   * Cholesky factorization of real symmetric
   * positive-definite matrix
   */
  nag_dpotrf(order, uplo, n, b, pdb, &fail);
  if (fail.code != NE_NOERROR)
    {
      fprintf(fpout, "Error from nag_dpotrf (f07fdc).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Reduce the problem to standard form C*y = lambda*y, storing */
  /* the result in A */
  /* nag_dsygst (f08sec).
   * Reduction to standard form of real symmetric-definite
   * generalized eigenproblem Ax~=~lambda~Bx, ABx~=~lambda~x
   * or BAx~=~lambda~x, B factorized by nag_dpotrf (f07fdc)
   */
  nag_dsygst(order, Nag_Compute_1, uplo, n, a, pda, b, pdb, &fail);
  if (fail.code != NE_NOERROR)
    {
      fprintf(fpout, "Error from nag_dsygst (f08sec).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Reduce C to tridiagonal form T = (Q**T)*C*Q */
  /* nag_dsytrd (f08fec).
   * Orthogonal reduction of real symmetric matrix to
   * symmetric tridiagonal form
   */
  nag_dsytrd(order, uplo, n, a, pda, d, e, tau, &fail);
  if (fail.code != NE_NOERROR)
    {
      fprintf(fpout, "Error from nag_dsytrd (f08fec).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Calculate the eigenvalues of T (same as C) */
  /* nag_dsterf (f08jfc).
   * All eigenvalues of real symmetric tridiagonal matrix,
   * root-free variant of QL or QR
   */
  nag_dsterf(n, d, e, &fail);
  if (fail.code != NE_NOERROR)
    {
      fprintf(fpout, "Error from nag_dsterf (f08jfc).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Print eigenvalues */
  fprintf(fpout, "Eigenvalues\n");
  for (i = 1; i <= n; ++i)
    fprintf(fpout, "%8.4f%s", d[i-1], i%9 == 0?"\n":" ");
  fprintf(fpout, "\n");
 END:
  if (fpin != stdin) fclose(fpin);
  if (fpout != stdout) fclose(fpout);
  if (a) NAG_FREE(a);
  if (b) NAG_FREE(b);
  if (d) NAG_FREE(d);
  if (e) NAG_FREE(e);
  if (tau) NAG_FREE(tau);

  return exit_status;
}