/* 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   uplo_char[2];
  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]
  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]
  order = Nag_RowMajor;
#endif

  INIT_FAIL(fail);
  Vprintf("nag_dsbtrd (f08hec) Example Program Results\n\n");

  /* Skip heading in data file */
  Vscanf("%*[^\n] ");
  Vscanf("%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)) )
    {
      Vprintf("Allocation failure\n");
      exit_status = -1;
      goto END;
    }

  /* Read A from data file */
  Vscanf(" ' %1s '%*[^\n] ", uplo_char);
  if (*(unsigned char *)uplo_char == 'L')
    uplo = Nag_Lower;
  else if (*(unsigned char *)uplo_char == 'U')
    uplo = Nag_Upper;
  else
    {
      Vprintf("Unrecognised character for Nag_UploType type\n");
      exit_status = -1;
      goto END;
    }
  k = kd + 1;
  if (uplo == Nag_Upper)
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = i; j <= MIN(i+kd,n); ++j)
            Vscanf("%lf", &AB_UPPER(i,j));
        }
      Vscanf("%*[^\n] ");
    }
  else
    {
      for (i = 1; i <= n; ++i)
        {
          for (j = MAX(1,i-kd); j <= i; ++j)
            Vscanf("%lf", &AB_LOWER(i,j));
        }
      Vscanf("%*[^\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)
    {
      Vprintf("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)
    {
      Vprintf("Error from nag_dsteqr (f08jec).\n%s\n", fail.message);
      exit_status = 1;
      goto END;
    }
  /* Print eigenvalues and eigenvectors */
  Vprintf("Eigenvalues\n");
  for (i = 1; i <= n; ++i)
    Vprintf("%8.4f%s", d[i-1], i%8==0 ?"\n":" ");
  Vprintf("\n\n");
  /* nag_gen_real_mat_print (x04cac).
   * Print real general matrix (easy-to-use)
   */
  nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n,
                         z, pdz, "Eigenvectors", 0, &fail);
  if (fail.code != NE_NOERROR)
    {
      Vprintf("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;
}