/* nag_lapackeig_dgehrd (f08nec) Example Program.
 *
 * Copyright 2024 Numerical Algorithms Group.
 *
 * Mark 30.1, 2024.
 */

#include <nag.h>
#include <stdio.h>

int main(void) {
  /* Scalars */
  Integer i, j, n, pda, tau_len;
  Integer exit_status = 0;
  NagError fail;
  Nag_OrderType order;
  /* Arrays */
  double *a = 0, *tau = 0;

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

  INIT_FAIL(fail);

  printf("nag_lapackeig_dgehrd (f08nec) Example Program Results\n\n");

  /* Skip heading in data file */
  scanf("%*[^\n] ");
  scanf("%" NAG_IFMT "%*[^\n] ", &n);

  pda = n;
  tau_len = n - 1;

  /* Allocate memory */
  if (!(a = NAG_ALLOC(n * n, double)) || !(tau = NAG_ALLOC(tau_len, double))) {
    printf("Allocation failure\n");
    exit_status = -1;
    goto END;
  }

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

  /* nag_lapackeig_dgehrd (f08nec): Reduce A to upper Hessenberg form */
  nag_lapackeig_dgehrd(order, n, 1, n, a, pda, tau, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_lapackeig_dgehrd (f08nec).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  /* Set the elements below the first subdiagonal to zero */
  for (i = 1; i <= n - 2; ++i) {
    for (j = i + 2; j <= n; ++j)
      A(j, i) = 0.0;
  }

  /* nag_file_print_matrix_real_gen (x04cac): Print upper Hessenberg form. */
  fflush(stdout);
  nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                                 n, a, pda, "Upper Hessenberg form", 0, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
           fail.message);
    exit_status = 1;
    goto END;
  }
END:
  NAG_FREE(a);
  NAG_FREE(tau);
  return exit_status;
}

#undef A