/* nag_lapackeig_dgels (f08aac) Example Program.
 *
 * Copyright 2024 Numerical Algorithms Group.
 *
 * Mark 30.2, 2024.
 */

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

int main(void) {
  /* Scalars */
  double rnorm;
  Integer exit_status = 0, i, j, m, n, nrhs, pda, pdb;
  /* Arrays */
  double *a = 0, *b = 0;
  /* Nag Types */
  Nag_OrderType order;
  NagError fail;

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

  INIT_FAIL(fail);

  printf("nag_lapackeig_dgels (f08aac) Example Program Results\n\n");

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

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

#ifdef NAG_COLUMN_MAJOR
  pda = m;
  pdb = MAX(m,n);
#else
  pda = n;
  pdb = nrhs;
#endif

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

  for (i = 1; i <= m; ++i)
    for (j = 1; j <= nrhs; ++j)
      scanf("%lf", &B(i, j));
  scanf("%*[^\n]");

  /* nag_lapackeig_dgels (f08aac).
   * Solve the least squares problem min( norm2(b - Ax) ) for x.
   */
  nag_lapackeig_dgels(order, Nag_NoTrans, m, n, nrhs, a, pda, b, pdb, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_lapackeig_dgels (f08aac).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  /* Print solution */
  printf("Least squares solution\n");
  for (i = 1; i <= n; ++i) {
    for (j = 1; j <= nrhs; ++j)
      printf("%11.4f%s", B(i, j), j % 7 == 0 ? "\n" : " ");
    printf("\n");
  }

  /* nag_blast_dge_norm (f16rac).
   * Compute and print estimate of the square root of the residual
   * sum of squares.
   */
  nag_blast_dge_norm(order, Nag_FrobeniusNorm, m - n, 1, &B(n + 1, 1), pdb,
                     &rnorm, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_blast_dge_norm (f16rac).\n%s\n", fail.message);
    exit_status = 1;
    goto END;
  }

  printf("\nSquare root of the residual sum of squares\n");
  printf("%11.2e\n", rnorm);

END:
  NAG_FREE(a);
  NAG_FREE(b);

  return exit_status;
}

#undef A
#undef B