/* nag_lapackeig_dsteqr (f08jec) Example Program.
 *
 * Copyright 2024 Numerical Algorithms Group.
 *
 * Mark 30.0, 2024.
 */

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

int main(void) {
  /* Scalars */
  Integer i, j, n, pdz, d_len, e_len;
  Integer exit_status = 0;
  /* Arrays */
  double *z = 0, *d = 0, *e = 0;
  /* Nag Types */
  NagError fail;
  Nag_OrderType order;

#ifdef NAG_COLUMN_MAJOR
#define Z(I, J) z[(J - 1) * pdz + I - 1]
  order = Nag_ColMajor;
#else
#define Z(I, J) z[(I - 1) * pdz + J - 1]
  order = Nag_RowMajor;
#endif

  INIT_FAIL(fail);

  printf("nag_lapackeig_dsteqr (f08jec) Example Program Results\n\n");

  /* Skip heading in data file */
  scanf("%*[^\n] ");
  scanf("%" NAG_IFMT "%*[^\n] ", &n);
  pdz = n;
  d_len = n;
  e_len = n - 1;

  /* Allocate memory */
  if (!(z = NAG_ALLOC(n * n, double)) || !(d = NAG_ALLOC(d_len, double)) ||
      !(e = NAG_ALLOC(e_len, double))) {
    printf("Allocation failure\n");
    exit_status = -1;
    goto END;
  }
  /* Read T from data file */
  for (i = 0; i < d_len; ++i)
    scanf("%lf", &d[i]);
  for (i = 0; i < e_len; ++i)
    scanf("%lf", &e[i]);
  /* Calculate all the eigenvalues and eigenvectors of tridiagonal matrix T,
   * reduced from real symmetric matrix using nag_lapackeig_dsteqr (f08jec).
   */
  nag_lapackeig_dsteqr(order, Nag_InitZ, n, d, e, z, pdz, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_lapackeig_dsteqr (f08jec).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  /* Standardize the eigenvectors so that first elements are non-negative. */
  for (j = 1; j <= n; j++) {
    if (Z(1, j) < 0.0) {
      for (i = 1; i <= n; i++)
        Z(i, j) = -Z(i, j);
    }
  }

  /* Print eigenvalues and eigenvectors */
  printf(" Eigenvalues\n");
  for (i = 0; i < n; ++i)
    printf("  %7.4f", d[i]);
  printf("\n\n");

  /* Print real general matrix Z using easy-to-use
   * nag_file_print_matrix_real_gen (x04cac).
   */
  fflush(stdout);
  nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                                 n, z, pdz, "Eigenvectors", 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;
  }

END:
  NAG_FREE(d);
  NAG_FREE(e);
  NAG_FREE(z);
  return exit_status;
}