/* nag_dsbtrd (f08hec) Example Program.
 *
 * Copyright 2001 Numerical Algorithms Group.
 *
 * Mark 7, 2001.
 */

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

int main(void)
{
  /* Scalars */
  Integer       i, j, k, kd, n, pdab, pdz, d_len, e_len;
  Integer       exit_status = 0;
  NagError      fail;
  Nag_UploType  uplo;
  Nag_OrderType order;
  /* Arrays */
  char          nag_enum_arg[40];
  double        *ab = 0, *d = 0, *e = 0, *z = 0;
  
#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 Z(I, J) z[(J - 1) * pdz + 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 Z(I, J) z[(I - 1) * pdz + J - 1]
  order = Nag_RowMajor;
#endif
  
  INIT_FAIL(fail);
  
  printf("nag_dsbtrd (f08hec) Example Program Results\n\n");
  
  /* Skip heading in data file */
  scanf("%*[^\n] ");
  scanf("%ld%ld%*[^\n] ", &n, &kd);
  pdab = kd + 1;
  pdz = n;
  d_len = n;
  e_len = n - 1;
  
  /* Allocate memory */
  if (!(ab = NAG_ALLOC(pdab * n, double)) ||
      !(d = NAG_ALLOC(d_len, double)) ||
      !(e = NAG_ALLOC(e_len, double)) ||
      !(z = NAG_ALLOC(pdz * n, double)))
    {
      printf("Allocation failure\n");
      exit_status = -1;
      goto END;
    }
  
  /* Read A from data file */
  scanf("%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);
  k = kd + 1;
  if (uplo == Nag_Upper)
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = i; j <= MIN(i + kd, n); ++j)
            scanf("%lf", &AB_UPPER(i, j));
        }
      scanf("%*[^\n] ");
    }
  else
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = MAX(1, i - kd); j <= i; ++j)
            scanf("%lf", &AB_LOWER(i, j));
        }
      scanf("%*[^\n] ");
    }
  
  /* Reduce A to tridiagonal form */
  /* nag_dsbtrd (f08hec).
   * Orthogonal reduction of real symmetric band matrix to
   * symmetric tridiagonal form
   */
  nag_dsbtrd(order, Nag_FormQ, uplo, n, kd, ab, pdab, d, e,
             z, pdz, &fail);
  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_dsbtrd (f08hec).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Calculate all the eigenvalues and eigenvectors of A */
  /* nag_dsteqr (f08jec).
   * All eigenvalues and eigenvectors of real symmetric
   * tridiagonal matrix, reduced from real symmetric matrix
   * using implicit QL or QR
   */
  nag_dsteqr(order, Nag_UpdateZ, n, d, e, z, pdz, &fail);
  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_dsteqr (f08jec).\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--)
        {
          Z(i, j) = Z(i, j) / Z(1,j);
        }
    }
  /* Print eigenvalues and eigenvectors */
  printf("Eigenvalues\n");
  for (i = 1; i <= n; ++i)
    printf("%8.4f%s", d[i-1], i%8 == 0?"\n":" ");
  printf("\n\n");
  /* nag_gen_real_mat_print (x04cac).
   * Print real general matrix (easy-to-use)
   */
  fflush(stdout);
  nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n,
                         z, pdz, "Eigenvectors", 0, &fail);
  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
             fail.message);
      exit_status = 1;
      goto END;
    }
 END:
  if (ab) NAG_FREE(ab);
  if (d) NAG_FREE(d);
  if (e) NAG_FREE(e);
  if (z) NAG_FREE(z);
  
  return exit_status;
}