NAG Library Manual, Mark 29.3
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NAG CL Interface Introduction
Example description
/* nag_sparse_complex_gen_precon_jacobi (f11dxc) Example Program.
 *
 * Copyright 2023 Numerical Algorithms Group.
 *
 * Mark 29.3, 2023.
 */
#include <math.h>
#include <nag.h>
int main(void) {
  /* Scalars */
  Integer exit_status = 0;
  double anorm, sigmax, stplhs, stprhs, tol;
  Integer i, irevcm, iterm, itn, lwork, lwreq, m, maxitn, monit, n, niter, nnz;
  /* Arrays */
  char nag_enum_arg[100];
  Complex *a = 0, *b = 0, *diag = 0, *work = 0, *x = 0;
  double *wgt = 0;
  Integer *icol = 0, *irow = 0;
  /* NAG types */
  Nag_InitializeA init;
  Nag_SparseNsym_Method method;
  Nag_SparseNsym_PrecType precon;
  Nag_NormType norm;
  Nag_SparseNsym_Weight weight;
  NagError fail, fail1;
  Integer verbose = 0;

  INIT_FAIL(fail);
  INIT_FAIL(fail1);

  printf(
      "nag_sparse_complex_gen_precon_jacobi (f11dxc) Example Program Results\n");
  /* Skip heading in data file */
  scanf("%*[^\n]");
  scanf("%" NAG_IFMT "%*[^\n]", &n);
  scanf("%" NAG_IFMT "%*[^\n]", &nnz);
  lwork = 300;
  if (!(a = NAG_ALLOC(nnz, Complex)) || !(b = NAG_ALLOC(n, Complex)) ||
      !(diag = NAG_ALLOC(n, Complex)) || !(work = NAG_ALLOC(lwork, Complex)) ||
      !(x = NAG_ALLOC(n, Complex)) || !(wgt = NAG_ALLOC(n, double)) ||
      !(icol = NAG_ALLOC(nnz, Integer)) || !(irow = NAG_ALLOC(nnz, Integer))) {
    printf("Allocation failure\n");
    exit_status = -1;
    goto END;
  }
  /* Read or initialize the parameters for the iterative solver */
  scanf("%99s%*[^\n]", nag_enum_arg);
  /* nag_enum_name_to_value (x04nac).
   * Converts NAG enum member name to value
   */
  method = (Nag_SparseNsym_Method)nag_enum_name_to_value(nag_enum_arg);
  scanf("%99s%*[^\n]", nag_enum_arg);
  precon = (Nag_SparseNsym_PrecType)nag_enum_name_to_value(nag_enum_arg);
  scanf("%99s%*[^\n]", nag_enum_arg);
  norm = (Nag_NormType)nag_enum_name_to_value(nag_enum_arg);
  scanf("%99s%*[^\n]", nag_enum_arg);
  weight = (Nag_SparseNsym_Weight)nag_enum_name_to_value(nag_enum_arg);
  scanf("%" NAG_IFMT "%*[^\n]", &iterm);
  scanf("%" NAG_IFMT "%lf%" NAG_IFMT "%*[^\n]", &m, &tol, &maxitn);
  scanf("%" NAG_IFMT "%*[^\n]", &monit);
  /* Read the parameters for the preconditioner */
  scanf("%" NAG_IFMT "%*[^\n]", &niter);
  anorm = 0.0;
  sigmax = 0.0;

  /* Read the nonzero elements of the matrix A */
  for (i = 0; i < nnz; i++)
    scanf(" ( %lf , %lf ) %" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &a[i].re,
          &a[i].im, &irow[i], &icol[i]);
    /* Read right-hand side vector b and initial approximate solution */
  for (i = 0; i < n; i++)
    scanf(" ( %lf , %lf )", &b[i].re, &b[i].im);
  scanf("%*[^\n]");
  for (i = 0; i < n; i++)
    scanf(" ( %lf , %lf )", &x[i].re, &x[i].im);
  scanf("%*[^\n]");

  /* Call to initialize the solver */
  /* nag_sparse_complex_gen_basic_setup (f11brc).
   * Complex sparse non-Hermitian linear systems, setup
   */
  nag_sparse_complex_gen_basic_setup(method, precon, norm, weight, iterm, n, m,
                                     tol, maxitn, anorm, sigmax, monit, &lwreq,
                                     work, lwork, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_sparse_complex_gen_basic_setup (f11brc).\n%s\n",
           fail.message);
    exit_status = 1;
    goto END;
  }
  /* Call solver repeatedly to solve the equations.
   * Note: the arrays b and x are overwritten; on final exit, x will
   *       contain the solution and b the residual vector.
   */
  irevcm = 0;
  init = Nag_InitializeI;
  while (irevcm != 4) {
    /* nag_sparse_complex_gen_basic_solver (f11bsc)
     * Complex sparse non-Hermitian linear systems, preconditioned RGMRES, CGS,
     * Bi-CGSTAB or TFQMR method
     */
    nag_sparse_complex_gen_basic_solver(&irevcm, x, b, wgt, work, lwreq, &fail);
    switch (irevcm) {
    case -1:
      /* nag_sparse_complex_gen_matvec (f11xnc)
       * Complex sparse non-Hermitian matrix vector multiply
       */
      nag_sparse_complex_gen_matvec(Nag_ConjTrans, n, nnz, a, irow, icol,
                                    Nag_SparseNsym_NoCheck, x, b, &fail1);
      break;
    case 1:
      nag_sparse_complex_gen_matvec(Nag_NoTrans, n, nnz, a, irow, icol,
                                    Nag_SparseNsym_NoCheck, x, b, &fail1);
      break;
    case 2:
      /* nag_sparse_complex_gen_precon_jacobi (f11dxc).
       * Complex sparse nonsymmetric linear systems, line Jacobi preconditioner
       */
      nag_sparse_complex_gen_precon_jacobi(
          Nag_SparseNsym_StoreCS, Nag_NoTrans, init, niter, n, nnz, a, irow,
          icol, Nag_SparseNsym_Check, x, b, diag, &fail1);
      init = Nag_InputA;
      break;
    case 3:
      /* nag_sparse_complex_gen_basic_diag (f11btc)
       * Complex sparse nonhermitian linear systems, diagnostic
       */
      nag_sparse_complex_gen_basic_diag(&itn, &stplhs, &stprhs, &anorm, &sigmax,
                                        work, lwreq, &fail1);
      if (fail1.code == NE_NOERROR && itn <= 3)
        printf("Monitoring at iteration number %2" NAG_IFMT "  "
               "order of residual norm %3" NAG_IFMT "\n",
               itn, (Integer)(log(stplhs) / log(10.0) + 0.5));
    }
    if (fail1.code != NE_NOERROR)
      irevcm = 6;
  }
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_sparse_complex_gen_basic_solver (f11bsc)\n%s\n",
           fail.message);
    exit_status = 2;
    goto END;
  }
  /* Obtain information about the computation using
   * nag_sparse_complex_gen_basic_diag (f11btc).
   * Complex sparse Hermitian linear systems, diagnostic.
   */
  nag_sparse_complex_gen_basic_diag(&itn, &stplhs, &stprhs, &anorm, &sigmax,
                                    work, lwreq, &fail);
  if (fail.code != NE_NOERROR) {
    printf("Error from nag_sparse_complex_gen_basic_diag (f11btc)\n%s\n",
           fail.message);
    exit_status = 3;
    goto END;
  }
  /* Print the output data */
  printf("\nFinal Results\n");
  if (verbose) {
    printf("Number of iterations for convergence:     %5" NAG_IFMT " \n", itn);
    printf("Residual norm:                            %11.1e \n", stplhs);
    printf("Right-hand side of termination criterion: %11.1e\n", stprhs);
    printf("1-norm of matrix A:                       %11.1e\n", anorm);
  }
  /* Output x */
  printf("\n    Solution vector\n");
  for (i = 0; i < n; i++)
    printf("(%8.3f, %8.3f)\n", x[i].re, x[i].im);
END:
  NAG_FREE(a);
  NAG_FREE(b);
  NAG_FREE(diag);
  NAG_FREE(work);
  NAG_FREE(x);
  NAG_FREE(wgt);
  NAG_FREE(icol);
  NAG_FREE(irow);
  return exit_status;
}