generic/solver/ida.c

/*  ASCEND modelling environment
    Copyright (C) 2006 Carnegie Mellon University

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2, or (at your option)
    any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.
*//**
    @file
    Access to the IDA integrator for ASCEND. IDA is a DAE solver that comes
    as part of the GPL-licensed SUNDIALS solver package from LLNL.
    @see http://www.llnl.gov/casc/sundials/
*//*
    by John Pye, May 2006
*/

/* 
    Be careful with the following. This file requires both the 'ida.h' from
    SUNDIALS as well as the 'ida.h' from ASCEND. Make sure that we're getting
    both of these; if you get problems check your build tool for the paths being
    passed to the C preprocessor.
*/

/* standard includes */
#include <signal.h>

/* ASCEND includes */
#include "ida.h"
#include <utilities/error.h>
#include <utilities/ascConfig.h>
#include <utilities/ascSignal.h>
#include <utilities/ascPanic.h>
#include <compiler/instance_enum.h>
#include "var.h"
#include "rel.h"
#include "discrete.h"
#include "conditional.h"
#include "logrel.h"
#include "bnd.h"
#include "linsol.h"
#include "linsolqr.h"
#include "slv_common.h"
#include "slv_client.h"
#include "relman.h"

/* SUNDIALS includes */
#ifdef ASC_WITH_IDA
# include <sundials/sundials_config.h>
# include <sundials/sundials_dense.h>
# include <ida/ida.h>
# include <nvector/nvector_serial.h>
# include <ida/ida_spgmr.h>
# include <ida/ida_dense.h>
# ifndef IDA_SUCCESS
#  error "Failed to include SUNDIALS IDA header file"
# endif
#endif

/*
    for the benefit of build tools that didn't sniff the SUNDIALS version, we
    assume version 2.2.x (and thence possible errors).
*/
#ifndef SUNDIALS_VERSION_MINOR
# ifdef __GNUC__
#  warning "GUESSING SUNDIALS VERSION 2.2"
# endif
# define SUNDIALS_VERSION_MINOR 2
#endif
#ifndef SUNDIALS_VERSION_MAJOR
# define SUNDIALS_VERSION_MAJOR 2
#endif

/* check that we've got what we expect now */
#ifndef ASC_IDA_H
# error "Failed to include ASCEND IDA header file"
#endif

#define FEX_DEBUG
#define JEX_DEBUG

/**
    Struct containing any stuff that IDA needs that doesn't fit into the 
    common IntegratorSystem struct.
*/
typedef struct{
    struct rel_relation **rellist;   /**< NULL terminated list of rels */
    struct var_variable **varlist;   /**< NULL terminated list of vars. ONLY USED FOR DEBUGGING -- get rid of it! */
    int nrels;
    int safeeval;                    /**< whether to pass the 'safe' flag to relman_eval */
} IntegratorIdaData;

/*-------------------------------------------------------------
  FORWARD DECLS
*/
/* residual function forward declaration */
int integrator_ida_fex(realtype tt, N_Vector yy, N_Vector yp, N_Vector rr, void *res_data);

int integrator_ida_jvex(realtype tt, N_Vector yy, N_Vector yp, N_Vector rr
        , N_Vector v, N_Vector Jv, realtype c_j
        , void *jac_data, N_Vector tmp1, N_Vector tmp2
);

/* error handler forward declaration */
void integrator_ida_error(int error_code
        , const char *module, const char *function
        , char *msg, void *eh_data
);

int integrator_ida_djex(long int Neq, realtype tt
        , N_Vector yy, N_Vector yp, N_Vector rr
        , realtype c_j, void *jac_data, DenseMat Jac
        , N_Vector tmp1, N_Vector tmp2, N_Vector tmp3
);

/*-------------------------------------------------------------
  SETUP/TEARDOWN ROUTINES
*/
void integrator_ida_create(IntegratorSystem *blsys){
    CONSOLE_DEBUG("ALLOCATING IDA ENGINE DATA");
    IntegratorIdaData *enginedata;
    enginedata = ASC_NEW(IntegratorIdaData);
    enginedata->rellist = NULL;
    enginedata->varlist = NULL;
    enginedata->safeeval = 1;
    blsys->enginedata = (void *)enginedata;
    integrator_ida_params_default(blsys);
}

void integrator_ida_free(void *enginedata){
    CONSOLE_DEBUG("DELETING IDA ENGINE DATA");
    IntegratorIdaData *d = (IntegratorIdaData *)enginedata;
    /* note, we don't own the rellist, so don't need to free it */
    ASC_FREE(d);
}

IntegratorIdaData *integrator_ida_enginedata(IntegratorSystem *blsys){
    IntegratorIdaData *d;
    assert(blsys!=NULL);
    assert(blsys->enginedata!=NULL);
    assert(blsys->engine==INTEG_IDA);
    d = ((IntegratorIdaData *)(blsys->enginedata));
    assert(d->safeeval = 1);
    return d;
}

/*-------------------------------------------------------------
  PARAMETERS FOR IDA
*/

enum ida_parameters{
    IDA_PARAM_LINSOLVER
    ,IDA_PARAM_AUTODIFF
    ,IDA_PARAM_RTOL
    ,IDA_PARAM_ATOL
    ,IDA_PARAM_ATOLVECT
    ,IDA_PARAM_GSMODIFIED
        ,IDA_PARAMS_SIZE
};

/**
    Here the full set of parameters is defined, along with upper/lower bounds,
    etc. The values are stuck into the blsys->params structure.

    @return 0 on success
*/
int integrator_ida_params_default(IntegratorSystem *blsys){
    asc_assert(blsys!=NULL);
    asc_assert(blsys->engine==INTEG_IDA);
    slv_parameters_t *p;
    p = &(blsys->params);

    slv_destroy_parms(p);

    if(p->parms==NULL){
        CONSOLE_DEBUG("params NULL");
        p->parms = ASC_NEW_ARRAY(struct slv_parameter, IDA_PARAMS_SIZE);
        if(p->parms==NULL)return -1;
        p->dynamic_parms = 1;
    }else{
        CONSOLE_DEBUG("params not NULL");
    }

    /* reset the number of parameters to zero so that we can check it at the end */
    p->num_parms = 0;

    slv_param_bool(p,IDA_PARAM_AUTODIFF
            ,(SlvParameterInitBool){{"autodiff"
            ,"Use auto-diff?",1
            ,"Use automatic differentiation of expressions (1) or use numerical derivatives (0)"
        }, TRUE}
    );

    slv_param_bool(p,IDA_PARAM_ATOLVECT
            ,(SlvParameterInitBool){{"atolvect"
            ,"Use 'ode_atol' values as specified?",1
            ,"If TRUE, values of 'ode_atol' are taken from your model and used "
            " in the integration. If FALSE, a scalar absolute tolerance value"
            " is shared by all variables. See IDA manual, section 5.5.1"
        }, TRUE }
    );

    slv_param_real(p,IDA_PARAM_ATOL
            ,(SlvParameterInitReal){{"atol"
            ,"Scalar absolute error tolerance",1
            ,"Value of the scalar absolute error tolerance. See also 'atolvect'."
            " See IDA manual, section 5.5.1"
        }, 1e-5, DBL_MIN, DBL_MAX }
    );

    slv_param_real(p,IDA_PARAM_RTOL
            ,(SlvParameterInitReal){{"rtol"
            ,"Scalar relative error tolerance",1
            ,"Value of the scalar relative error tolerance."
            " See IDA manual, section 5.5.1"
        }, 1e-4, DBL_MIN, DBL_MAX }
    );

    slv_param_char(p,IDA_PARAM_LINSOLVER
            ,(SlvParameterInitChar){{"linsolver"
            ,"Linear solver",1
            ,"See IDA manual, section 5.5.3."
        }, "SPGMR"}, (char *[]){"DENSE","SPGMR",NULL}
    );

    slv_param_bool(p,IDA_PARAM_GSMODIFIED
            ,(SlvParameterInitBool){{"gsmodified"
            ,"Use modified Gram-Schmidt orthogonalisation in SPGMR?",2
            ,"TRUE = GS_MODIFIED, FALSE = GS_CLASSICAL. See IDA manual section 5.5.6.6"
        }, TRUE}
    );

    asc_assert(p->num_parms == IDA_PARAMS_SIZE);

    CONSOLE_DEBUG("Created %d params", p->num_parms);

    return 0;
}

/*-------------------------------------------------------------
  MAIN IDA SOLVER ROUTINE, see IDA manual, sec 5.4, p. 27 ff.
*/

/* return 1 on success */
int integrator_ida_solve(
        IntegratorSystem *blsys
        , unsigned long start_index
        , unsigned long finish_index
){
    void *ida_mem;
    int size, flag, t_index;
    realtype t0, reltol, abstol, t, tret, tout1;
    N_Vector y0, yp0, abstolvect, ypret, yret;
    IntegratorIdaData *enginedata;
    char *linsolver;

    CONSOLE_DEBUG("STARTING IDA...");

    enginedata = integrator_ida_enginedata(blsys);
    CONSOLE_DEBUG("safeeval = %d",enginedata->safeeval);

    /* store reference to list of relations (in enginedata) */
    enginedata->nrels = slv_get_num_solvers_rels(blsys->system);
    enginedata->rellist = slv_get_solvers_rel_list(blsys->system);
    enginedata->varlist = slv_get_solvers_var_list(blsys->system);
    CONSOLE_DEBUG("Number of relations: %d",enginedata->nrels);
    CONSOLE_DEBUG("Number of dependent vars: %ld",blsys->n_y);
    size = blsys->n_y;

    if(enginedata->nrels!=size){
        ERROR_REPORTER_HERE(ASC_USER_ERROR,"Integration problem is not square (%d rels, %d vars)", enginedata->nrels, size);
        return 0; /* failure */
    }

    /* retrieve initial values from the system */
    
    /** @TODO fix this, the starting time != first sample */
    t0 = integrator_get_t(blsys);
    CONSOLE_DEBUG("RETRIEVED t0 = %f",t0);

    CONSOLE_DEBUG("RETRIEVING y0");

    y0 = N_VNew_Serial(size);
    integrator_get_y(blsys,NV_DATA_S(y0));

    CONSOLE_DEBUG("RETRIEVING yp0");

    yp0 = N_VNew_Serial(size);
    integrator_get_ydot(blsys,NV_DATA_S(yp0));

    N_VPrint_Serial(yp0);
    CONSOLE_DEBUG("yp0 is at %p",&yp0);

    /* create IDA object */
    ida_mem = IDACreate();

    /* relative error tolerance */  
    reltol = SLV_PARAM_REAL(&(blsys->params),IDA_PARAM_RTOL);
    CONSOLE_DEBUG("rtol = %8.2e",reltol);

    /* allocate internal memory */
    if(SLV_PARAM_BOOL(&(blsys->params),IDA_PARAM_ATOLVECT)){
        /* vector of absolute tolerances */
        CONSOLE_DEBUG("USING VECTOR OF ATOL VALUES");
        abstolvect = N_VNew_Serial(size);
        integrator_get_atol(blsys,NV_DATA_S(abstolvect));

        flag = IDAMalloc(ida_mem, &integrator_ida_fex, t0, y0, yp0, IDA_SV, reltol, abstolvect);

        N_VDestroy_Serial(abstolvect);
    }else{
        /* scalar absolute tolerance (one value for all) */
        CONSOLE_DEBUG("USING SCALAR ATOL VALUE = %8.2e",abstol);
        abstol = SLV_PARAM_REAL(&(blsys->params),IDA_PARAM_ATOL);
        flag = IDAMalloc(ida_mem, &integrator_ida_fex, t0, y0, yp0, IDA_SS, reltol, &abstol);
    }

    if(flag==IDA_MEM_NULL){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"ida_mem is NULL");
        return 0;
    }else if(flag==IDA_MEM_FAIL){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Unable to allocate memory (IDAMalloc)");
        return 0;
    }else if(flag==IDA_ILL_INPUT){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Invalid input to IDAMalloc");
        return 0;
    }/* else success */

    /* set optional inputs... */
    IDASetErrHandlerFn(ida_mem, &integrator_ida_error, (void *)blsys);
    IDASetRdata(ida_mem, (void *)blsys);
    IDASetMaxStep(ida_mem, integrator_get_maxstep(blsys));  
    IDASetInitStep(ida_mem, integrator_get_stepzero(blsys));
    IDASetMaxNumSteps(ida_mem, integrator_get_maxsubsteps(blsys));
    if(integrator_get_minstep(blsys)>0){
        ERROR_REPORTER_HERE(ASC_PROG_NOTE,"IDA does not support minstep (ignored)\n");
    }
    /* there's no capability for setting *minimum* step size in IDA */


    /* attach linear solver module, using the default value of maxl */
    linsolver = SLV_PARAM_CHAR(&(blsys->params),IDA_PARAM_LINSOLVER);
    CONSOLE_DEBUG("ASSIGNING LINEAR SOLVER '%s'",linsolver);
    if(strcmp(linsolver,"SPGMR")==0){
        CONSOLE_DEBUG("USING 'SCALED PRECONDITIONER GMRES' LINEAR SOLVER");
        flag = IDASpgmr(ida_mem, 0);
        if(flag==IDASPILS_MEM_NULL){
            ERROR_REPORTER_HERE(ASC_PROG_ERR,"ida_mem is NULL");
            return 0;
        }else if(flag==IDASPILS_MEM_FAIL){
            ERROR_REPORTER_HERE(ASC_PROG_ERR,"Unable to allocate memory (IDASpgmr)");
            return 0;
        }/* else success */

        /* assign the J*v function */
        if(SLV_PARAM_BOOL(&(blsys->params),IDA_PARAM_AUTODIFF)){
            CONSOLE_DEBUG("USING AUTODIFF");
            flag = IDASpilsSetJacTimesVecFn(ida_mem, &integrator_ida_jvex, (void *)blsys);
            if(flag==IDASPILS_MEM_NULL){
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"ida_mem is NULL");
                return 0;
            }else if(flag==IDASPILS_LMEM_NULL){
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"IDASPILS linear solver has not been initialized");
                return 0;
            }/* else success */
        }else{
            CONSOLE_DEBUG("USING NUMERICAL DIFF");
        }

        /* select Gram-Schmidt orthogonalisation */
        if(SLV_PARAM_BOOL(&(blsys->params),IDA_PARAM_GSMODIFIED)){
            CONSOLE_DEBUG("USING MODIFIED GS");
            flag = IDASpilsSetGSType(ida_mem,MODIFIED_GS);
            if(flag!=IDASPILS_SUCCESS){
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"Failed to set GS_MODIFIED");
                return 0;
            }
        }else{
            CONSOLE_DEBUG("USING CLASSICAL GS");
            flag = IDASpilsSetGSType(ida_mem,CLASSICAL_GS);
            if(flag!=IDASPILS_SUCCESS){
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"Failed to set GS_MODIFIED");
                return 0;
            }
        }
    }else if(strcmp(linsolver,"DENSE")==0){
        CONSOLE_DEBUG("DENSE DIRECT SOLVER, size = %d",size);
        flag = IDADense(ida_mem, size);
        switch(flag){
            case IDADENSE_SUCCESS: break;
            case IDADENSE_MEM_NULL: ERROR_REPORTER_HERE(ASC_PROG_ERR,"ida_mem is NULL"); return 0;
            case IDADENSE_ILL_INPUT: ERROR_REPORTER_HERE(ASC_PROG_ERR,"IDADENSE is not compatible with current nvector module"); return 0;
            case IDADENSE_MEM_FAIL: ERROR_REPORTER_HERE(ASC_PROG_ERR,"Memory allocation failed for IDADENSE"); return 0;
            default: ERROR_REPORTER_HERE(ASC_PROG_ERR,"bad return"); return 0;
        }
        
        if(SLV_PARAM_BOOL(&(blsys->params),IDA_PARAM_AUTODIFF)){
            CONSOLE_DEBUG("USING AUTODIFF");
            flag = IDADenseSetJacFn(ida_mem, &integrator_ida_djex, (void *)blsys);
            switch(flag){
                case IDADENSE_SUCCESS: break;
                default: ERROR_REPORTER_HERE(ASC_PROG_ERR,"Failed IDADenseSetJacFn"); return 0;
            }
        }else{
            CONSOLE_DEBUG("USING NUMERICAL DIFF");
        }
    }else{
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Unknown IDA linear solver choice '%s'",linsolver);
        return 0;
    }

    /* set linear solver optional inputs...

        ...nothing here at the moment... 

    */

#if 0
    /* correct initial values, given derivatives */
    blsys->currentstep=0;
    t_index=start_index;
    tout1 = samplelist_get(blsys->samples, t_index);

    CONSOLE_DEBUG("SOLVING INITIAL CONDITIONS IDACalcIC (tout1 = %f)", tout1);

# if SUNDIALS_VERSION_MAJOR==2 && SUNDIALS_VERSION_MINOR==3
    /* note the new API from version 2.3 and onwards */
    flag = IDACalcIC(ida_mem, IDA_Y_INIT, tout1);
# else
    flag = IDACalcIC(ida_mem, t0, y0, yp0, IDA_Y_INIT, tout1);
# endif

    if(flag!=IDA_SUCCESS){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Unable to solve initial values (IDACalcIC)");
        return 0;
    }/* else success */

    CONSOLE_DEBUG("INITIAL CONDITIONS SOLVED :-)");
#endif

    /* optionally, specify ROO-FINDING PROBLEM */

    /* -- set up the IntegratorReporter */
    integrator_output_init(blsys);

    /* -- store the initial values of all the stuff */
    integrator_output_write(blsys);
    integrator_output_write_obs(blsys);

    /* specify where the returned values should be stored */
    yret = y0;
    ypret = yp0;

    /* advance solution in time, return values as yret and derivatives as ypret */
    blsys->currentstep=1;
    for(t_index=start_index;t_index <= finish_index;++t_index, ++blsys->currentstep){
        t = samplelist_get(blsys->samples, t_index);

        /* CONSOLE_DEBUG("SOLVING UP TO t = %f", t); */
    
        flag = IDASolve(ida_mem, t, &tret, yret, ypret, IDA_NORMAL);

        /* pass the values of everything back to the compiler */
        integrator_set_t(blsys, (double)tret);
        integrator_set_y(blsys, NV_DATA_S(yret));
        integrator_set_ydot(blsys, NV_DATA_S(ypret));

        if(flag<0){
            ERROR_REPORTER_HERE(ASC_PROG_ERR,"Failed to solve t = %f (IDASolve), error %d", t, flag);
            break;
        }

        /* -- do something so that blsys knows the values of tret, yret and ypret */

        /* -- store the current values of all the stuff */
        integrator_output_write(blsys);
        integrator_output_write_obs(blsys);
    }

    /* -- close the IntegratorReporter */
    integrator_output_close(blsys);

    if(flag < 0){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Solving aborted while attempting t = %f", t);
        return 0;
    }

    /* get optional outputs */
    
    /* free solution memory */
    N_VDestroy_Serial(yret);
    N_VDestroy_Serial(ypret);
    
    /* free solver memory */
    IDAFree(ida_mem);

    /* all done */
    return 1;
}

/*--------------------------------------------------
  RESIDUALS AND JACOBIAN
*/
/**
    Function to evaluate system residuals, in the form required for IDA.

    Given tt, yy and yp, we need to evaluate and return rr.

    @param tt current value of indep variable (time)
    @param yy current values of dependent variable vector
    @param yp current values of derivatives of dependent variables
    @param rr the output residual vector (is we're returning data to)
    @param res_data pointer to our stuff (blsys in this case).

    @return 0 on success, positive on recoverable error, and
        negative on unrecoverable error.
*/
int integrator_ida_fex(realtype tt, N_Vector yy, N_Vector yp, N_Vector rr, void *res_data){
    IntegratorSystem *blsys;
    IntegratorIdaData *enginedata;
    int i, calc_ok, is_error;
    struct rel_relation** relptr;
    double resid;
    char *relname;
#ifdef FEX_DEBUG
    char *varname;
#endif

    blsys = (IntegratorSystem *)res_data;
    enginedata = integrator_ida_enginedata(blsys);

#ifdef FEX_DEBUG
    /* fprintf(stderr,"\n\n"); */
    CONSOLE_DEBUG("EVALUTE RESIDUALS...");
#endif

    /* pass the values of everything back to the compiler */
    integrator_set_t(blsys, (double)tt);
    integrator_set_y(blsys, NV_DATA_S(yy));
    integrator_set_ydot(blsys, NV_DATA_S(yp));

    if(NV_LENGTH_S(rr)!=enginedata->nrels){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Invalid residuals nrels!=length(rr)");
        return -1; /* unrecoverable */
    }

    /**
        @TODO does this function (fex) do bounds checking already?
    */

    /* evaluate each residual in the rellist */
    is_error = 0; 
    relptr = enginedata->rellist;

    Asc_SignalHandlerPush(SIGFPE,SIG_IGN);
    if (setjmp(g_fpe_env)==0) {
        for(i=0, relptr = enginedata->rellist;
                i< enginedata->nrels && relptr != NULL;
                ++i, ++relptr
        ){
            resid = relman_eval(*relptr, &calc_ok, enginedata->safeeval);

            NV_Ith_S(rr,i) = resid;
            if(!calc_ok){
                relname = rel_make_name(blsys->system, *relptr);
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"Calculation error in rel '%s'",relname);
                ASC_FREE(relname);
                /* presumable some output already made? */
                is_error = 1;
            }
        }
    }else{
        relname = rel_make_name(blsys->system, *relptr);
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Floating point error (SIGFPE) in rel '%s'",relname);
        ASC_FREE(relname);
        is_error = 1;
    }
    Asc_SignalHandlerPop(SIGFPE,SIG_IGN);

#ifdef FEX_DEBUG
    /* output residuals to console */
    CONSOLE_DEBUG("RESIDUAL OUTPUT");
    fprintf(stderr,"index\t%20s\t%20s\t%s\n","y","ydot","resid");
    for(i=0; i<blsys->n_y; ++i){
        varname = var_make_name(blsys->system,blsys->y[i]);
        fprintf(stderr,"%d\t%10s=%10f\t",i,varname,NV_Ith_S(yy,i));
        if(blsys->ydot[i]){
            varname = var_make_name(blsys->system,blsys->ydot[i]);
            fprintf(stderr,"%10s=%10f\t",varname,NV_Ith_S(yp,i));
        }else{
            fprintf(stderr,"diff(%4s)=%10f\t",varname,NV_Ith_S(yp,i));
        }
        ASC_FREE(varname);
        relname = rel_make_name(blsys->system,enginedata->rellist[i]);
        fprintf(stderr,"'%s'=%f\n",relname,NV_Ith_S(rr,i));
    }
#endif

    if(is_error){
        return 1;
    }

#ifdef FEX_DEBUG    
    CONSOLE_DEBUG("RESIDUAL OK");
#endif
    return 0;
}

/**
    Dense Jacobian evaluation. Only suitable for small problems!
*/
int integrator_ida_djex(long int Neq, realtype tt
        , N_Vector yy, N_Vector yp, N_Vector rr
        , realtype c_j, void *jac_data, DenseMat Jac
        , N_Vector tmp1, N_Vector tmp2, N_Vector tmp3
){
    IntegratorSystem *blsys;
    IntegratorIdaData *enginedata;
    char *relname;
#ifdef JEX_DEBUG
    char *varname;
#endif
    int status;
    struct rel_relation **relptr;
    int i;
    var_filter_t filter = {VAR_SVAR, VAR_SVAR};
    double *derivatives;
    int *variables;
    int count, j, var_yindex;

    blsys = (IntegratorSystem *)jac_data;
    enginedata = integrator_ida_enginedata(blsys);

    /* allocate space for returns from relman_diff2: we *should* be able to use 'tmp1' and 'tmp2' here... */
    variables = ASC_NEW_ARRAY(int, NV_LENGTH_S(yy) * 2);
    derivatives = ASC_NEW_ARRAY(double, NV_LENGTH_S(yy) * 2);

    /* pass the values of everything back to the compiler */
    integrator_set_t(blsys, (double)tt);
    integrator_set_y(blsys, NV_DATA_S(yy));
    integrator_set_ydot(blsys, NV_DATA_S(yp));

#ifdef JEX_DEBUG
    /* print vars */
    for(i=0; i < blsys->n_y; ++i){
        varname = var_make_name(blsys->system, blsys->y[i]);
        CONSOLE_DEBUG("%s = %f = %f",varname,NV_Ith_S(yy,i),var_value(blsys->y[i]));
        ASC_FREE(varname);
    }

    /* print derivatives */
    for(i=0; i < blsys->n_y; ++i){
        if(blsys->ydot[i]){
            varname = var_make_name(blsys->system, blsys->ydot[i]);
            CONSOLE_DEBUG("%s = %f =%f",varname,NV_Ith_S(yp,i),var_value(blsys->ydot[i]));
            ASC_FREE(varname);
        }else{
            varname = var_make_name(blsys->system, blsys->y[i]);
            CONSOLE_DEBUG("diff(%s) = %f",varname,NV_Ith_S(yp,i));
            ASC_FREE(varname);
        }
    }

    /* print step size */
    CONSOLE_DEBUG("<c_j> = %f",c_j);
#endif
    
    /* build up the dense jacobian matrix... */
    status = 0;
    for(i=0, relptr = enginedata->rellist;
            i< enginedata->nrels && relptr != NULL;
            ++i, ++relptr
    ){
        /* get derivatives for this particular relation */
        status = relman_diff2(*relptr, &filter, derivatives, variables, &count, enginedata->safeeval);

        if(status){
            relname = rel_make_name(blsys->system, *relptr);
            CONSOLE_DEBUG("ERROR calculating derivatives for relation '%s'",relname);
            ASC_FREE(relname);
            break;
        }

        /* output what's going on here ... */
#ifdef JEX_DEBUG
        relname = rel_make_name(blsys->system, *relptr);
        CONSOLE_DEBUG("RELATION %d '%s'",i,relname);
        fprintf(stderr,"%d: '%s': ",i,relname);
        ASC_FREE(relname);
        for(j=0;j<count;++j){
            varname = var_make_name(blsys->system, enginedata->varlist[variables[j]]);
            var_yindex = blsys->y_id[variables[j]];
            if(var_yindex >=0){
                fprintf(stderr,"  var[%d]='%s'=y[%d]",variables[j],varname,var_yindex);
            }else{
                fprintf(stderr,"  var[%d]='%s'=ydot[%d]",variables[j],varname,-var_yindex-1);
            }
            ASC_FREE(varname);
        }
        fprintf(stderr,"\n");
#endif  
        /* insert values into the Jacobian row in appropriate spots (can assume Jac starts with zeros -- IDA manual) */
        for(j=0; j < count; ++j){           
            var_yindex = blsys->y_id[variables[j]];
            if(var_yindex >= 0){
                asc_assert(blsys->y[var_yindex]==enginedata->varlist[variables[j]]);
                DENSE_ELEM(Jac,i,var_yindex) += derivatives[j];
            }else{
                asc_assert(blsys->ydot[-var_yindex-1]==enginedata->varlist[variables[j]]);
                DENSE_ELEM(Jac,i,-var_yindex-1) += derivatives[j] * c_j;
            }
        }
    }

#ifdef JEX_DEBUG
    CONSOLE_DEBUG("PRINTING JAC");
    fprintf(stderr,"\t");
    for(j=0; j < blsys->n_y; ++j){
        if(j)fprintf(stderr,"\t");
        varname = var_make_name(blsys->system,blsys->y[j]);
        fprintf(stderr,"%11s",varname);
        ASC_FREE(varname);
    }
    fprintf(stderr,"\n");
    for(i=0; i < enginedata->nrels; ++i){
        relname = rel_make_name(blsys->system, enginedata->rellist[i]);
        fprintf(stderr,"%s\t",relname);
        ASC_FREE(relname);

        for(j=0; j < blsys->n_y; ++j){
            if(j)fprintf(stderr,"\t");
            fprintf(stderr,"%11.2e",DENSE_ELEM(Jac,i,j));
        }
        fprintf(stderr,"\n");
    }   
#endif

    if(status){
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"There were derivative evaluation errors in the dense jacobian");
        return 1;
    }

#ifdef FEX_DEBUG
    CONSOLE_DEBUG("DJEX RETURNING 0");
#endif
    return 0;
}

/**
    Function to evaluate the product J*v, in the form required for IDA (see IDASpilsSetJacTimesVecFn)

    Given tt, yy, yp, rr and v, we need to evaluate and return Jv.

    @param tt current value of the independent variable (time, t)
    @param yy current value of the dependent variable vector, y(t).
    @param yp current value of y'(t).
    @param rr current value of the residual vector F(t, y, y').
    @param v  the vector by which the Jacobian must be multiplied to the right.
    @param Jv the output vector computed
    @param c_j the scalar in the system Jacobian, proportional to the inverse of the step size ($ \alpha$ in Eq. (3.5) ).
    @param jac_data pointer to our stuff (blsys in this case, passed into IDA via IDASp*SetJacTimesVecFn.)
    @param tmp1 @see tmp2
    @param tmp2 (as well as tmp1) pointers to memory allocated for variables of type N_Vector for use here as temporary storage or work space.
    @return 0 on success
*/
int integrator_ida_jvex(realtype tt, N_Vector yy, N_Vector yp, N_Vector rr
        , N_Vector v, N_Vector Jv, realtype c_j
        , void *jac_data, N_Vector tmp1, N_Vector tmp2
){
    IntegratorSystem *blsys;
    IntegratorIdaData *enginedata;
    int i, j, is_error=0;
    struct rel_relation** relptr;
    char *relname, *varname;
    int status;
    double Jv_i;
    int var_yindex;

    int *variables;
    double *derivatives;
    var_filter_t filter;
    int count;

#ifdef JEX_DEBUG
    CONSOLE_DEBUG("EVALUATING JACOBIAN...");
#endif

    blsys = (IntegratorSystem *)jac_data;
    enginedata = integrator_ida_enginedata(blsys);

    /* pass the values of everything back to the compiler */
    integrator_set_t(blsys, (double)tt);
    integrator_set_y(blsys, NV_DATA_S(yy));
    integrator_set_ydot(blsys, NV_DATA_S(yp));
    /* no real use for residuals (rr) here, I don't think? */

    /* allocate space for returns from relman_diff2: we *should* be able to use 'tmp1' and 'tmp2' here... */
    variables = ASC_NEW_ARRAY(int, NV_LENGTH_S(yy) * 2);
    derivatives = ASC_NEW_ARRAY(double, NV_LENGTH_S(yy) * 2);

    /* evaluate the derivatives... */
    /* J = dG_dy = dF_dy + alpha * dF_dyp */

    filter.matchbits = VAR_SVAR;
    filter.matchvalue = VAR_SVAR;

    Asc_SignalHandlerPush(SIGFPE,SIG_IGN);
    if (setjmp(g_fpe_env)==0) {
        for(i=0, relptr = enginedata->rellist;
                i< enginedata->nrels && relptr != NULL;
                ++i, ++relptr
        ){
            /* get derivatives for this particular relation */
            status = relman_diff2(*relptr, &filter, derivatives, variables, &count, enginedata->safeeval);
            /* CONSOLE_DEBUG("Got derivatives against %d matching variables", count); */

            if(status){
                relname = rel_make_name(blsys->system, *relptr);
                ERROR_REPORTER_HERE(ASC_PROG_ERR,"Calculation error in rel '%s'",relname);
                ASC_FREE(relname);
                is_error = 1;
                break;
            }

            /*
                Now we have the derivatives wrt each alg/diff variable in the
                present equation. variables[] points into the varlist. need
                a mapping from the varlist to the y and ydot lists.
            */

            Jv_i = 0;
            for(j=0; j < count; ++j){
                /* CONSOLE_DEBUG("j = %d, variables[j] = %d, n_y = %ld", j, variables[j], blsys->n_y);
                varname = var_make_name(blsys->system, enginedata->varlist[variables[j]]);
                if(varname){
                    CONSOLE_DEBUG("Variable %d '%s' derivative = %f", variables[j],varname,derivatives[j]);
                    ASC_FREE(varname);
                }else{
                    CONSOLE_DEBUG("Variable %d (UNKNOWN!): derivative = %f",variables[j],derivatives[j]);
                }
                */
                
                var_yindex = blsys->y_id[variables[j]];
                /* CONSOLE_DEBUG("j = %d: variables[j] = %d, y_id = %d",j,variables[j],var_yindex); */

                if(var_yindex >= 0){
#ifdef JEX_DEBUG
                    asc_assert(blsys->y[var_yindex]==enginedata->varlist[variables[j]]);
                    fprintf(stderr,"Jv[%d] += %f (dF[%d]/dy[%d] = %f, v[%d] = %f)\n", i
                        , derivatives[j] * NV_Ith_S(v,var_yindex)
                        , i, var_yindex, derivatives[j]
                        , var_yindex, NV_Ith_S(v,var_yindex)
                    );
#endif
                    Jv_i += derivatives[j] * NV_Ith_S(v,var_yindex);
                }else{
#ifdef JEX_DEBUG
                    fprintf(stderr,"Jv[%d] += %f (dF[%d]/dydot[%d] = %f, v[%d] = %f)\n", i
                        , derivatives[j] * NV_Ith_S(v,-var_yindex-1)
                        , i, -var_yindex-1, derivatives[j]
                        , -var_yindex-1, NV_Ith_S(v,-var_yindex-1)
                    );
#endif
                    asc_assert(blsys->ydot[-var_yindex-1]==enginedata->varlist[variables[j]]);
                    Jv_i += derivatives[j] * NV_Ith_S(v,-var_yindex-1) * c_j; 
                }
            }

            NV_Ith_S(Jv,i) = Jv_i;
#ifdef JEX_DEBUG
            relname = rel_make_name(blsys->system, *relptr);
            CONSOLE_DEBUG("'%s': Jv[%d] = %f", relname, i, NV_Ith_S(Jv,i));
            ASC_FREE(relname);
            return 1;           
#endif
        }
    }else{
        relname = rel_make_name(blsys->system, *relptr);
        ERROR_REPORTER_HERE(ASC_PROG_ERR,"Floating point error (SIGFPE) in rel '%s'",relname);
        ASC_FREE(relname);
        is_error = 1;
    }
    Asc_SignalHandlerPop(SIGFPE,SIG_IGN);

    if(is_error){
        CONSOLE_DEBUG("SOME ERRORS FOUND IN EVALUATION");
        return 1;
    }
    return 0;
}

/*----------------------------------------------
  ERROR REPORTING
*/
/**
    Error message reporter function to be passed to IDA. All error messages
    will trigger a call to this function, so we should find everything
    appearing on the console (in the case of Tcl/Tk) or in the errors/warnings
    panel (in the case of PyGTK).
*/
void integrator_ida_error(int error_code
        , const char *module, const char *function
        , char *msg, void *eh_data
){
    IntegratorSystem *blsys;
    error_severity_t sev;

    /* cast back the IntegratorSystem, just in case we need it */
    blsys = (IntegratorSystem *)eh_data;

    /* severity depends on the sign of the error_code value */
    if(error_code <= 0){
        sev = ASC_PROG_ERR;
    }else{
        sev = ASC_PROG_WARNING;
    }

    /* use our all-purpose error reporting to get stuff back to the GUI */
    error_reporter(sev,module,0,function,"%s (error %d)",msg,error_code);
}