/* nag_linsys_real_tridiag_solve (f04bcc) Example Program.
 *
 * Copyright 2023 Numerical Algorithms Group.
 *
 * Mark 29.2, 2023.
 */

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

int main(void) {
  /* Scalars */
  double errbnd, rcond;
  Integer exit_status, i, j, n, nrhs, pdb;

  /* Arrays */
  double *b = 0, *d = 0, *dl = 0, *du = 0, *du2 = 0;
  Integer *ipiv = 0;

  /* Nag Types */
  NagError fail;
  Nag_OrderType order;

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

  exit_status = 0;
  INIT_FAIL(fail);

  printf("nag_linsys_real_tridiag_solve (f04bcc) Example Program Results\n\n");

  /* Skip heading in data file */
  scanf("%*[^\n] ");
  scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &nrhs);
  if (n >= 0 && nrhs >= 0) {
    /* Allocate memory */
    if (!(b = NAG_ALLOC(n * nrhs, double)) || !(d = NAG_ALLOC(n, double)) ||
        !(dl = NAG_ALLOC(n - 1, double)) || !(du = NAG_ALLOC(n - 1, double)) ||
        !(du2 = NAG_ALLOC(n - 2, double)) || !(ipiv = NAG_ALLOC(n, Integer))) {
      printf("Allocation failure\n");
      exit_status = -1;
      goto END;
    }
#ifdef NAG_COLUMN_MAJOR
    pdb = n;
#else
    pdb = nrhs;
#endif
  } else {
    printf("%s\n", "n and/or nrhs too small");
    exit_status = 1;
    return exit_status;
  }
  /* Read A and B from data file */
  for (i = 1; i <= n - 1; ++i) {
    scanf("%lf", &du[i - 1]);
  }
  scanf("%*[^\n] ");

  for (i = 1; i <= n; ++i) {
    scanf("%lf", &d[i - 1]);
  }
  scanf("%*[^\n] ");

  for (i = 1; i <= n - 1; ++i) {
    scanf("%lf", &dl[i - 1]);
  }
  scanf("%*[^\n] ");

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

  /* Solve the equations AX = B for X */
  /* nag_linsys_real_tridiag_solve (f04bcc).
   * Computes the solution and error-bound to a real
   * tridiagonal system of linear equations
   */
  nag_linsys_real_tridiag_solve(order, n, nrhs, dl, d, du, du2, ipiv, b, pdb,
                                &rcond, &errbnd, &fail);
  if (fail.code == NE_NOERROR) {
    /* Print solution, estimate of condition number and approximate */
    /* error bound */
    /* nag_file_print_matrix_real_gen (x04cac).
     * Print real general matrix (easy-to-use)
     */
    fflush(stdout);
    nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                                   nrhs, b, pdb, "Solution", 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;
    }
    printf("\n");
    printf("%s\n      %10.1e\n", "Estimate of condition number", 1.0 / rcond);
    printf("\n\n");

    printf("%s\n      %10.1e\n\n",
           "Estimate of error bound for computed solutions", errbnd);
  } else if (fail.code == NE_RCOND) {
    /* Matrix A is numerically singular.  Print estimate of */
    /* reciprocal of condition number and solution */

    printf("\n%s\n%6s%10.1e\n\n\n",
           "Estimate of reciprocal of condition number", "", rcond);
    /* nag_file_print_matrix_real_gen (x04cac), see above. */
    fflush(stdout);
    nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
                                   nrhs, b, pdb, "Solution", 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;
    }
  } else if (fail.code == NE_SINGULAR) {
    /* The upper triangular matrix U is exactly singular.  Print */
    /* details of factorization */

    printf("%s\n\n", "Details of factorization");
    printf("%s\n", " Second superdiagonal of U");

    for (i = 1; i <= n - 2; ++i) {
      printf("%9.4f%s", du2[i - 1], i % 8 == 0 || i == n - 2 ? "\n" : " ");
    }
    printf("\n");

    printf("\n%s\n", " First superdiagonal of U");
    for (i = 1; i <= n - 1; ++i) {
      printf("%9.4f%s", du[i - 1], i % 8 == 0 || i == n - 1 ? "\n" : " ");
    }
    printf("\n\n");

    printf("%s\n", " Main diagonal of U");
    for (i = 1; i <= n; ++i) {
      printf("%9.4f%s", d[i - 1], i % 8 == 0 || i == n ? "\n" : " ");
    }
    printf("\n\n");

    printf("%s\n", " Multipliers");
    for (i = 1; i <= n - 1; ++i) {
      printf("%9.4f%s", dl[i - 1], i % 8 == 0 || i == n - 1 ? "\n" : " ");
    }
    printf("\n\n");

    printf("%s\n", " Vector of interchanges");
    for (i = 1; i <= n; ++i) {
      printf("%9" NAG_IFMT "%s", ipiv[i - 1],
             i % 8 == 0 || i == n ? "\n" : " ");
    }
    printf("\n");
  } else {
    printf("Error from nag_linsys_real_tridiag_solve (f04bcc).\n%s\n",
           fail.message);
    exit_status = 1;
    goto END;
  }
END:
  NAG_FREE(b);
  NAG_FREE(d);
  NAG_FREE(dl);
  NAG_FREE(du);
  NAG_FREE(du2);
  NAG_FREE(ipiv);

  return exit_status;
}