/* nag_lapackeig_dstedc (f08jhc) Example Program.
 *
 * Copyright 2024 Numerical Algorithms Group.
 *
 * Mark 30.2, 2024.
 */

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

int main(void) {
  /* Scalars */
  Integer i, j, k, kd, n, pdab, pdq;
  Integer exit_status = 0;
  /* Arrays */
  char nag_enum_arg[40];
  double *ab = 0, *d = 0, *e = 0, *q = 0;
  /* Nag Types */
  Nag_OrderType order;
  Nag_UploType uplo;
  NagError fail;

#ifdef NAG_COLUMN_MAJOR
#define AB_UPPER(I, J) ab[(J - 1) * pdab + k + I - J - 1]
#define AB_LOWER(I, J) ab[(J - 1) * pdab + I - J]
#define Q(I, J) q[(J - 1) * pdq + I - 1]
  order = Nag_ColMajor;
#else
#define AB_UPPER(I, J) ab[(I - 1) * pdab + J - I]
#define AB_LOWER(I, J) ab[(I - 1) * pdab + k + J - I - 1]
#define Q(I, J) q[(I - 1) * pdq + J - 1]
  order = Nag_RowMajor;
#endif

  INIT_FAIL(fail);

  printf("nag_lapackeig_dstedc (f08jhc) Example Program Results\n\n");

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

  /* Read uplo */
  scanf("%39s%*[^\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);

  pdab = kd + 1;

#ifdef NAG_COLUMN_MAJOR
  pdq = n;
#else
  pdq = n;
#endif

  /* Allocate memory */
  if (!(ab = NAG_ALLOC(pdab * n, double)) || !(d = NAG_ALLOC(n, double)) ||
      !(e = NAG_ALLOC(n - 1, double)) || !(q = NAG_ALLOC(n * n, double))) {
    printf("Allocation failure\n");
    exit_status = -1;
    goto END;
  }

  /* Read the upper or lower triangular part of the band matrix A
   * from data file.
   */
  k = kd + 1;
  if (uplo == Nag_Upper) {
    for (i = 1; i <= n; ++i)
      for (j = i; j <= MIN(n, i + kd); ++j)
        scanf("%lf", &AB_UPPER(i, j));
    scanf("%*[^\n]");
  } else if (uplo == Nag_Lower) {
    for (i = 1; i <= n; ++i)
      for (j = MAX(1, i - kd); j <= i; ++j)
        scanf("%lf", &AB_LOWER(i, j));
    scanf("%*[^\n]");
  }

  /* nag_lapackeig_dsbtrd (f08hec).
   * Reduce A to tridiagonal form T = (Q^T)*A*Q, and form Q.
   */
  nag_lapackeig_dsbtrd(order, Nag_FormQ, uplo, n, kd, ab, pdab, d, e, q, pdq,
                       &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_lapackeig_dsbtrd (f08hec).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  /* nag_lapackeig_dstedc (f08jhc)
   * Calculate all the eigenvalues and eigenvectors of A,
   * from T and Q.
   */
  nag_lapackeig_dstedc(order, Nag_OrigEigVecs, n, d, e, q, pdq, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_lapackeig_dstedc (f08jhc).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  /* Normalize the eigenvectors */
  for (j = 1; j <= n; j++)
    for (i = n; i >= 1; i--)
      Q(i, j) = Q(i, j) / Q(1, j);

  /* Print eigenvalues and eigenvectors */
  printf("%s\n", "Eigenvalues");
  for (i = 0; i < n; ++i)
    printf("%8.4f%s", d[i], (i + 1) % 8 == 0 ? "\n" : " ");
  printf("\n\n");

  /* nag_file_print_matrix_real_gen (x04cac).
   * Print eigenvectors.
   */
  fflush(stdout);
  nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                                 n, q, pdq, "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;
    goto END;
  }

END:
  NAG_FREE(ab);
  NAG_FREE(d);
  NAG_FREE(e);
  NAG_FREE(q);

  return exit_status;
}

#undef AB_UPPER
#undef AB_LOWER
#undef Q