/*---------------------------------------------------------------
 * Programmer(s): Cody J. Balos @ LLNL
 *                Daniel R. Reynolds @ SMU
 *---------------------------------------------------------------
 * SUNDIALS Copyright Start
 * Copyright (c) 2002-2022, Lawrence Livermore National Security
 * and Southern Methodist University.
 * All rights reserved.
 *
 * See the top-level LICENSE and NOTICE files for details.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 * SUNDIALS Copyright End
 *---------------------------------------------------------------
 * Example problem:
 *
 * The following test simulates a brusselator problem from chemical
 * kinetics.  This is n PDE system with 3 components, Y = [u,v,w],
 * satisfying the equations,
 *    u_t = du*u_xx + a - (w+1)*u + v*u^2
 *    v_t = dv*v_xx + w*u - v*u^2
 *    w_t = dw*w_xx + (b-w)/ep - w*u
 * for t in [0, 10], x in [0, 1], with initial conditions
 *    u(0,x) =  a  + 0.1*sin(pi*x)
 *    v(0,x) = b/a + 0.1*sin(pi*x)
 *    w(0,x) =  b  + 0.1*sin(pi*x),
 * and with stationary boundary conditions, i.e.
 *    u_t(t,0) = u_t(t,1) = 0,
 *    v_t(t,0) = v_t(t,1) = 0,
 *    w_t(t,0) = w_t(t,1) = 0.
 * Note: these can also be implemented as Dirichlet boundary
 * conditions with values identical to the initial conditions.
 *
 * The spatial derivatives are computed using second-order
 * centered differences, with the data distributed over N points
 * on a uniform spatial grid.
 *
 * The data is stored using the ManyVector structure for a
 * structure-of-arrays format, i.e., each of u, v and w are
 * stored in separate serial vectors, and are attached together
 * using the ManyVector infrastructure.
 *
 * This program solves the problem with the ARK method, treating
 * only the reaction terms implicitly (diffusion is treated
 * explicitly), using a Newton iteration with the SUNSPGMR
 * iterative linear solver, and a user-supplied
 * Jacobian-vector-product routine.
 *
 * 100 outputs are printed at equal intervals, and run statistics
 * are printed at the end.
 *---------------------------------------------------------------*/

/* Header files */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <arkode/arkode_arkstep.h>     /* prototypes for ARKStep fcts., consts */
#include <nvector/nvector_manyvector.h>/* manyvector N_Vector types, fcts. etc */
#include <nvector/nvector_serial.h>    /* serial N_Vector types, fcts., macros */
#include <sunlinsol/sunlinsol_spgmr.h> /* access to SPGMR SUNLinearSolver      */
#include <sundials/sundials_types.h>   /* defs. of realtype, sunindextype, etc */

#if defined(SUNDIALS_EXTENDED_PRECISION)
#define GSYM "Lg"
#define ESYM "Le"
#define FSYM "Lf"
#else
#define GSYM "g"
#define ESYM "e"
#define FSYM "f"
#endif

/* realtype constant macros */
#define ZERO RCONST(0.0)
#define ONE  RCONST(1.0)
#define TWO  RCONST(2.0)

/* user data structure */
typedef struct {
  sunindextype N;  /* number of intervals     */
  realtype dx;     /* mesh spacing            */
  realtype a;      /* constant forcing on u   */
  realtype b;      /* steady-state value of w */
  realtype du;     /* diffusion coeff for u   */
  realtype dv;     /* diffusion coeff for v   */
  realtype dw;     /* diffusion coeff for w   */
  realtype ep;     /* stiffness parameter     */
} *UserData;

/* User-supplied Functions Called by the Solver */
static int fe(realtype t, N_Vector y, N_Vector ydot, void *user_data);
static int fi(realtype t, N_Vector y, N_Vector ydot, void *user_data);
static int JacVI(N_Vector v, N_Vector Jv, realtype t, N_Vector y,
                 N_Vector fy, void *user_data, N_Vector tmp1);

/* Private function to check function return values */
static int check_flag(void *flagvalue, const char *funcname, int opt);

/* Main Program */
int main()
{
  /* general problem parameters */
  realtype T0 = ZERO;                /* initial time */
  realtype Tf = RCONST(10.0);        /* final time */
  int Nt = 100;                      /* total number of output times */
  int Nvar = 3;                      /* number of solution fields */
  UserData userdata = NULL;
  realtype *udata, *vdata, *wdata;
  sunindextype N = 201;              /* spatial mesh size */
  realtype a = RCONST(0.6);          /* problem parameters */
  realtype b = RCONST(2.0);
  realtype du = RCONST(0.001);
  realtype dv = RCONST(0.001);
  realtype dw = RCONST(0.001);
  realtype ep = RCONST(1.0e-5);      /* stiffness parameter */
  realtype reltol = RCONST(1.0e-6);  /* tolerances */
  realtype abstol = RCONST(1.0e-10);
  sunindextype i;

  /* general problem variables */
  int flag;                     /* reusable error-checking flag */
  N_Vector y = NULL;            /* empty manyvector for storing solution */
  N_Vector u = NULL;            /* empty vectors for storing solution components */
  N_Vector v = NULL;
  N_Vector w = NULL;
  N_Vector uvw[3];              /* vector array composed of u,v,w component vectors */
  SUNLinearSolver LS = NULL;    /* empty linear solver object */
  void *arkode_mem = NULL;      /* empty ARKode memory structure */
  realtype pi, t, dTout, tout, unorm, vnorm, wnorm;
  FILE *FID, *UFID, *VFID, *WFID;
  int iout;
  long int nst, nst_a, nfe, nfi, nsetups, nli, nlcf, nJv, nfeLS, nni, ncfn, netf;

  /* Create the SUNDIALS context object for this simulation */
  SUNContext ctx;
  flag = SUNContext_Create(NULL, &ctx);
  if (check_flag(&flag, "SUNContext_Create", 1)) return 1;

  /* allocate udata structure */
  userdata = (UserData) malloc(sizeof(*userdata));
  if (check_flag((void *) userdata, "malloc", 2)) return 1;

  /* store the inputs in the UserData structure */
  userdata->N  = N;
  userdata->a  = a;
  userdata->b  = b;
  userdata->du = du;
  userdata->dv = dv;
  userdata->dw = dw;
  userdata->ep = ep;

  /* Initial problem output */
  printf("\n1D Brusselator PDE test problem:\n");
  printf("    N = %li\n", (long int) userdata->N);
  printf("    problem parameters:  a = %"GSYM",  b = %"GSYM",  ep = %"GSYM"\n",
      userdata->a, userdata->b, userdata->ep);
  printf("    diffusion coefficients:  du = %"GSYM",  dv = %"GSYM",  dw = %"GSYM"\n",
      userdata->du, userdata->dv, userdata->dw);
  printf("    reltol = %.1"ESYM",  abstol = %.1"ESYM"\n\n", reltol, abstol);

  /* Initialize data structures */
  userdata->dx = ONE/(N-1);      /* set spatial mesh spacing */
  u = N_VNew_Serial(N, ctx);     /* Create serial vectors */
  if (check_flag((void *) u, "N_VNew_Serial", 0)) return 1;
  v = N_VClone(u);
  if (check_flag((void *) v, "N_VClone", 0)) return 1;
  w = N_VClone(u);
  if (check_flag((void *) w, "N_VClone", 0)) return 1;

  /* Create manyvector for solution */
  uvw[0] = u; uvw[1] = v; uvw[2] = w;
  y = N_VNew_ManyVector(Nvar, uvw, ctx);
  if (check_flag((void *)y, "N_VNew_ManyVector", 0)) return 1;

  udata = N_VGetArrayPointer(u);     /* Access data array for new NVector u */
  if (check_flag((void *)udata, "N_VGetArrayPointer", 0)) return 1;
  vdata = N_VGetArrayPointer(v);     /* Access data array for new NVector v */
  if (check_flag((void *)vdata, "N_VGetArrayPointer", 0)) return 1;
  wdata = N_VGetArrayPointer(w);     /* Access data array for new NVector w */
  if (check_flag((void *)wdata, "N_VGetArrayPointer", 0)) return 1;

  /* Set initial conditions into y */
  pi = RCONST(4.0)*atan(ONE);
  for (i=0; i<N; i++) {
    udata[i] =  a  + RCONST(0.1)*sin(pi*i*userdata->dx);  /* u */
    vdata[i] = b/a + RCONST(0.1)*sin(pi*i*userdata->dx);  /* v */
    wdata[i] =  b  + RCONST(0.1)*sin(pi*i*userdata->dx);  /* w */
  }

  /* Call ARKStepCreate to initialize the ARK timestepper module and
     specify the right-hand side function in y'=f(t,y), the inital time
     T0, and the initial dependent variable vector y.  Note: since this
     problem is fully implicit, we set f_E to NULL and f_I to f. */
  arkode_mem = ARKStepCreate(fe, fi, T0, y, ctx);
  if (check_flag((void *)arkode_mem, "ARKStepCreate", 0)) return 1;

  /* Set routines */
  flag = ARKStepSetUserData(arkode_mem, (void *) userdata);  /* Pass udata to user functions */
  if (check_flag(&flag, "ARKStepSetUserData", 1)) return 1;
  flag = ARKStepSStolerances(arkode_mem, reltol, abstol);    /* Specify tolerances */
  if (check_flag(&flag, "ARKStepSStolerances", 1)) return 1;

  /* Initialize spgmr solver */
  LS = SUNLinSol_SPGMR(y, SUN_PREC_NONE, 10, ctx);
  if (check_flag((void *)LS, "SUNLinSol_SPGMR", 0)) return 1;

  /* Linear solver interface */
  flag = ARKStepSetLinearSolver(arkode_mem, LS, NULL);       /* Attach linear solver */
  if (check_flag(&flag, "ARKStepSetLinearSolver", 1)) return 1;
  flag = ARKStepSetJacTimes(arkode_mem, NULL, JacVI);        /* Set the Jacobian-vector product */
  if (check_flag(&flag, "ARKStepSetJacTimes", 1)) return 1;

  /* output spatial mesh to disk */
  FID = fopen("bruss_mesh.txt","w");
  for (i=0; i<N; i++)  fprintf(FID,"  %.16"ESYM"\n", userdata->dx*i);
  fclose(FID);

  /* Open output streams for results, access data array */
  UFID=fopen("bruss_u.txt","w");
  VFID=fopen("bruss_v.txt","w");
  WFID=fopen("bruss_w.txt","w");

  /* output initial condition to disk */
  for (i=0; i<N; i++)  fprintf(UFID," %.16"ESYM"", udata[i]);
  for (i=0; i<N; i++)  fprintf(VFID," %.16"ESYM"", vdata[i]);
  for (i=0; i<N; i++)  fprintf(WFID," %.16"ESYM"", wdata[i]);
  fprintf(UFID,"\n");
  fprintf(VFID,"\n");
  fprintf(WFID,"\n");

  /* Main time-stepping loop: calls ARKStepEvolve to perform the integration, then
     prints results.  Stops when the final time has been reached */
  t = T0;
  dTout = (Tf-T0)/Nt;
  tout = T0+dTout;
  printf("        t      ||u||_rms   ||v||_rms   ||w||_rms\n");
  printf("   ----------------------------------------------\n");
  for (iout=0; iout<Nt; iout++) {

    /* call integrator */
    flag = ARKStepEvolve(arkode_mem, tout, y, &t, ARK_NORMAL);
    if (check_flag(&flag, "ARKStepEvolve", 1)) break;

    /* print solution statistics */
    unorm = N_VDotProd(u,u);
    unorm = sqrt(unorm/N);
    vnorm = N_VDotProd(v,v);
    vnorm = sqrt(vnorm/N);
    wnorm = N_VDotProd(w,w);
    wnorm = sqrt(wnorm/N);
    printf("  %10.6"FSYM"  %10.6"FSYM"  %10.6"FSYM"  %10.6"FSYM"\n", t, unorm, vnorm, wnorm);

    /* check integrator flag */
    if (flag >= 0) {    /* successful solve: update output time */
      tout += dTout;
      tout = (tout > Tf) ? Tf : tout;
    } else {            /* unsuccessful solve: break */
      fprintf(stderr,"Solver failure, stopping integration\n");
      break;
    }

    /* output results to disk */
    for (i=0; i<N; i++)  fprintf(UFID," %.16"ESYM"", udata[i]);
    for (i=0; i<N; i++)  fprintf(VFID," %.16"ESYM"", vdata[i]);
    for (i=0; i<N; i++)  fprintf(WFID," %.16"ESYM"", wdata[i]);
    fprintf(UFID,"\n");
    fprintf(VFID,"\n");
    fprintf(WFID,"\n");
  }
  printf("   ----------------------------------------------\n");
  fclose(UFID);
  fclose(VFID);
  fclose(WFID);

  /* Print some final statistics */
  flag = ARKStepGetNumSteps(arkode_mem, &nst);
  check_flag(&flag, "ARKStepGetNumSteps", 1);
  flag = ARKStepGetNumStepAttempts(arkode_mem, &nst_a);
  check_flag(&flag, "ARKStepGetNumStepAttempts", 1);
  flag = ARKStepGetNumRhsEvals(arkode_mem, &nfe, &nfi);
  check_flag(&flag, "ARKStepGetNumRhsEvals", 1);
  flag = ARKStepGetNumLinSolvSetups(arkode_mem, &nsetups);
  check_flag(&flag, "ARKStepGetNumLinSolvSetups", 1);
  flag = ARKStepGetNumErrTestFails(arkode_mem, &netf);
  check_flag(&flag, "ARKStepGetNumErrTestFails", 1);
  flag = ARKStepGetNumNonlinSolvIters(arkode_mem, &nni);
  check_flag(&flag, "ARKStepGetNumNonlinSolvIters", 1);
  flag = ARKStepGetNumNonlinSolvConvFails(arkode_mem, &ncfn);
  check_flag(&flag, "ARKStepGetNumNonlinSolvConvFails", 1);
  flag = ARKStepGetNumLinIters(arkode_mem, &nli);
  check_flag(&flag, "ARKStepGetNumLinIters", 1);
  flag = ARKStepGetNumLinConvFails(arkode_mem, &nlcf);
  check_flag(&flag, "ARKStepGetNumLinConvFails", 1);
  flag = ARKStepGetNumJtimesEvals(arkode_mem, &nJv);
  check_flag(&flag, "ARKStepGetNumJtimesEvals", 1);
  flag = ARKStepGetNumLinRhsEvals(arkode_mem, &nfeLS);
  check_flag(&flag, "ARKStepGetNumLinRhsEvals", 1);

  printf("\nFinal Solver Statistics:\n");
  printf("   Internal solver steps = %li (attempted = %li)\n", nst, nst_a);
  printf("   Total RHS evals:  Fe = %li,  Fi = %li\n", nfe, nfi);
  printf("   Total linear solver setups = %li\n", nsetups);
  printf("   Total linear iterations = %li\n", nli);
  printf("   Total linear convergence failures = %li\n", nlcf);
  printf("   Total J*v evaluations = %li\n", nJv);
  printf("   Total RHS evals in linear solver = %li\n", nfeLS);
  printf("   Total number of Newton iterations = %li\n", nni);
  printf("   Total number of nonlinear solver convergence failures = %li\n", ncfn);
  printf("   Total number of error test failures = %li\n\n", netf);

  /* Clean up and return with successful completion */
  N_VDestroy(y);                /* Free vectors */
  N_VDestroy(u);
  N_VDestroy(v);
  N_VDestroy(w);
  free(userdata);               /* Free user data */
  ARKStepFree(&arkode_mem);     /* Free integrator memory */
  SUNLinSolFree(LS);            /* Free linear solver */
  SUNContext_Free(&ctx);        /* Free context */

  return 0;
}

/*-------------------------------
 * Functions called by the solver
 *-------------------------------*/

/* fe routine to compute the diffusion portion of the ODE RHS. */
static int fe(realtype t, N_Vector y, N_Vector ydot, void *user_data)
{
  UserData userdata = (UserData) user_data;      /* access problem data */
  sunindextype N = userdata->N;                  /* set variable shortcuts */
  realtype du = userdata->du;
  realtype dv = userdata->dv;
  realtype dw = userdata->dw;
  realtype dx = userdata->dx;
  realtype *y_u=NULL, *y_v=NULL, *y_w=NULL;
  realtype *f_u=NULL, *f_v=NULL, *f_w=NULL;
  realtype uconst, vconst, wconst;
  sunindextype i;

  y_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 0));
  if (check_flag((void *) y_u, "N_VGetArrayPointer", 0)) return 1;
  y_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 1));
  if (check_flag((void *) y_v, "N_VGetArrayPointer", 0)) return 1;
  y_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 2));
  if (check_flag((void *) y_w, "N_VGetArrayPointer", 0)) return 1;

  f_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 0));
  if (check_flag((void *) f_u, "N_VGetArrayPointer", 0)) return 1;
  f_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 1));
  if (check_flag((void *) f_v, "N_VGetArrayPointer", 0)) return 1;
  f_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 2));
  if (check_flag((void *) f_w, "N_VGetArrayPointer", 0)) return 1;

  N_VConst(RCONST(0.0), ydot);              /* initialize ydot to zero */

  /* iterate over domain, computing all equations */
  uconst = du/dx/dx;
  vconst = dv/dx/dx;
  wconst = dw/dx/dx;
  for (i=1; i<N-1; i++) {

    /* Fill in ODE RHS for u */
    f_u[i] = (y_u[i-1] - TWO*y_u[i] + y_u[i+1])*uconst;

    /* Fill in ODE RHS for v */
    f_v[i] = (y_v[i-1] - TWO*y_v[i] + y_v[i+1])*vconst;

    /* Fill in ODE RHS for w */
    f_w[i] = (y_w[i-1] - TWO*y_w[i] + y_w[i+1])*wconst;
  }

  /* enforce stationary boundaries */
  f_u[0]   = f_v[0]   = f_w[0]   = ZERO;
  f_u[N-1] = f_v[N-1] = f_w[N-1] = ZERO;

  return 0;     /* Return with success */
}

/* fi routine to compute the reaction portion of the ODE RHS. */
static int fi(realtype t, N_Vector y, N_Vector ydot, void *user_data)
{
  UserData userdata = (UserData) user_data;      /* access problem data */
  sunindextype N = userdata->N;                  /* set variable shortcuts */
  realtype a  = userdata->a;
  realtype b  = userdata->b;
  realtype ep = userdata->ep;
  realtype *y_u=NULL, *y_v=NULL, *y_w=NULL;
  realtype *f_u=NULL, *f_v=NULL, *f_w=NULL;
  sunindextype i;

  y_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 0));
  if (check_flag((void *) y_u, "N_VGetArrayPointer", 0)) return 1;
  y_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 1));
  if (check_flag((void *) y_v, "N_VGetArrayPointer", 0)) return 1;
  y_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 2));
  if (check_flag((void *) y_w, "N_VGetArrayPointer", 0)) return 1;

  f_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 0));
  if (check_flag((void *) f_u, "N_VGetArrayPointer", 0)) return 1;
  f_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 1));
  if (check_flag((void *) f_v, "N_VGetArrayPointer", 0)) return 1;
  f_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(ydot, 2));
  if (check_flag((void *) f_w, "N_VGetArrayPointer", 0)) return 1;

  N_VConst(0.0, ydot);                        /* initialize ydot to zero */

  /* iterate over domain, computing all equations */
  for (i=1; i<N-1; i++) {

    /* Fill in ODE RHS for u */
    f_u[i] = a - (y_w[i]+ONE)*y_u[i] + y_v[i]*y_u[i]*y_u[i];

    /* Fill in ODE RHS for v */
    f_v[i] = y_w[i]*y_u[i] - y_v[i]*y_u[i]*y_u[i];

    /* Fill in ODE RHS for w */
    f_w[i] = (b-y_w[i])/ep - y_w[i]*y_u[i];
  }

  /* enforce stationary boundaries */
  f_u[0]   = f_v[0]   = f_w[0]   = ZERO;
  f_u[N-1] = f_v[N-1] = f_w[N-1] = ZERO;

  return 0;     /* Return with success */
}

/* Jacobian-vector product routine (implicit portion only) */
static int JacVI(N_Vector v, N_Vector Jv, realtype t, N_Vector y,
                 N_Vector fy, void *user_data, N_Vector tmp1)
{
  UserData userdata = (UserData) user_data;      /* access problem data */
  sunindextype N = userdata->N;                  /* set variable shortcuts */
  realtype ep = userdata->ep;
  realtype *y_u=NULL, *y_v=NULL, *y_w=NULL;
  realtype *v_u=NULL, *v_v=NULL, *v_w=NULL;
  realtype *Ju_v=NULL, *Jv_v=NULL, *Jw_v=NULL;
  sunindextype i;

  y_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 0));
  if (check_flag((void *) y_u, "N_VGetArrayPointer", 0)) return 1;
  y_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 1));
  if (check_flag((void *) y_v, "N_VGetArrayPointer", 0)) return 1;
  y_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(y, 2));
  if (check_flag((void *) y_w, "N_VGetArrayPointer", 0)) return 1;

  v_u = N_VGetArrayPointer(N_VGetSubvector_ManyVector(v, 0));
  if (check_flag((void *) v_u, "N_VGetArrayPointer", 0)) return 1;
  v_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(v, 1));
  if (check_flag((void *) v_v, "N_VGetArrayPointer", 0)) return 1;
  v_w = N_VGetArrayPointer(N_VGetSubvector_ManyVector(v, 2));
  if (check_flag((void *) v_w, "N_VGetArrayPointer", 0)) return 1;

  Ju_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(Jv, 0));
  if (check_flag((void *) Ju_v, "N_VGetArrayPointer", 0)) return 1;
  Jv_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(Jv, 1));
  if (check_flag((void *) Jv_v, "N_VGetArrayPointer", 0)) return 1;
  Jw_v = N_VGetArrayPointer(N_VGetSubvector_ManyVector(Jv, 2));
  if (check_flag((void *) Jw_v, "N_VGetArrayPointer", 0)) return 1;

  N_VConst(ZERO, Jv);      /* initialize Jv to zero */

  /* iterate over domain, computing Jacobian-vector products */
  for (i=1; i<N-1; i++) {

    /* Fill in Jacobian-vector product for Ju*v */
    Ju_v[i] = - v_w[i]*y_u[i] - y_w[i]*v_u[i] - v_u[i] + v_v[i]*y_u[i]*y_u[i] + TWO*y_v[i]*y_u[i]*v_u[i];

    /* Fill in Jacobian-vector product for Jv*v */
    Jv_v[i] = v_w[i]*y_u[i] + y_w[i]*v_u[i] - v_v[i]*y_u[i]*y_u[i] - TWO*y_v[i]*y_u[i]*v_u[i];

    /* Fill in Jacobian-vector product for Jw*v */
    Jw_v[i] = - v_w[i]/ep - v_w[i]*y_u[i] - y_w[i]*v_u[i];

  }

  /* enforce stationary boundaries */
  Ju_v[0]   = Jv_v[0]   = Jw_v[0]   = ZERO;
  Ju_v[N-1] = Jv_v[N-1] = Jw_v[N-1] = ZERO;

  return 0;                                  /* Return with success */
}

/*-------------------------------
 * Private helper functions
 *-------------------------------*/

/* Check function return value...
    opt == 0 means SUNDIALS function allocates memory so check if
             returned NULL pointer
    opt == 1 means SUNDIALS function returns a flag so check if
             flag < 0
    opt == 2 means function allocates memory so check if returned
             NULL pointer
*/
static int check_flag(void *flagvalue, const char *funcname, int opt)
{
  int *errflag;

  /* Check if SUNDIALS function returned NULL pointer - no memory allocated */
  if (opt == 0 && flagvalue == NULL) {
    fprintf(stderr, "\nSUNDIALS_ERROR: %s() failed - returned NULL pointer\n\n",
            funcname);
    return 1; }

  /* Check if flag < 0 */
  else if (opt == 1) {
    errflag = (int *) flagvalue;
    if (*errflag < 0) {
      fprintf(stderr, "\nSUNDIALS_ERROR: %s() failed with flag = %d\n\n",
              funcname, *errflag);
      return 1; }}

  /* Check if function returned NULL pointer - no memory allocated */
  else if (opt == 2 && flagvalue == NULL) {
    fprintf(stderr, "\nMEMORY_ERROR: %s() failed - returned NULL pointer\n\n",
            funcname);
    return 1; }

  return 0;
}


/*---- end of file ----*/