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/* This file is part of Cloudy and is copyright (C)1979-2011 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */
/*HeatSum evaluate heating and secondary ionization for current conditions */
/*HeatZero is called by ConvBase */
#include "cddefines.h"
#include "physconst.h"
#include "thermal.h"
#include "heavy.h"
#include "trace.h"
#include "secondaries.h"
#include "conv.h"
#include "called.h"
#include "coolheavy.h"
#include "iso.h"
#include "mole.h"
#include "h2.h"
#include "hmi.h"
#include "dense.h"
#include "ionbal.h"
#include "phycon.h"
#include "numderiv.h"
#include "atomfeii.h"
#include "cooling.h"
#include "grainvar.h"
#include "taulines.h"
#include "deuterium.h"

/* this is the faintest relative heating we will print */
static const double FAINT_HEAT = 0.02;

static const bool PRT_DERIV = false;

void HeatSum( void )
{
        /* use to dim some vectors */
        const int NDIM = 40;

        /* secondary ionization and excitation due to Compton scattering */
        double cosmic_ray_ionization_rate , 
                pair_production_ionization_rate , 
                fast_neutron_ionization_rate , SecExcitLyaRate;

        /* ionization and excitation rates from hydrogen itself */
        double SeconIoniz_iso[NISO] , 
                SeconExcit_iso[NISO];

        long int i, 
          ion,
          ipnt, 
          ipsave[NDIM], 
          j, 
          jpsave[NDIM], 
          limit;

        double HeatingLo ,
                HeatingHi ,
                secmet ,
                smetla;
        long ipISO,
                ns;
        static long int nhit=0, 
          nzSave=0;
        double photo_heat_2lev_atoms,
                photo_heat_ISO_atoms ,
                photo_heat_UTA ,
                OtherHeat , 
                deriv, 
                oldfac, 
                save[NDIM];
        static double oldheat=0., 
          oldtemp=0.;
        double secmetsave[LIMELM];

        realnum SaveOxygen1 , SaveCarbon1;

        /* routine to sum up total heating, and print agents if needed
         * it also computes the true derivative, dH/dT */
        double Cosmic_ray_heat_eff ,
                Cosmic_ray_sec2prim;
        realnum sec2prim_par_1;
        realnum sec2prim_par_2;

        DEBUG_ENTRY( "HeatSum()" );

        /*******************************************************************
         *
         * reevaluate the secondary ionization and excitation rates 
         *
         *******************************************************************/
        /* ElectronFraction is electron fraction 
         * analytic fits to 
         * >>>refer     sec     ioniz   Shull & Van Steenberg (1985; Ap.J. 298, 268).
         * lgSecOFF turns off secondary ionizations, sets heating efficiency to 100% */

        /* at very low ionization - as per 
         * >>>refer     sec     ioniz   Xu & McCray 1991, Ap.J. 375, 190.
         * everything goes to asymptote that is not present in Shull and
         * Van Steenberg - do this by not letting ElecFrac fall below 1e-4 */
        /* this uses the correct electron density, which will not equal the
         * current electron density if we are not converged.  Using the 
         * correct value aids convergence onto it */
        
        // ElectronFraction should be the fraction of electrons available
        // for collisions which are free, as opposed to bound in atoms,
        // ions or molecules, which seems like the most plausible
        // generalization of the definition of X in S&vS.

        realnum xValenceDonorDensity, ElectronFraction;

        if (1)
        {
                long ipNoble[] = { 
                        ipHELIUM, ipNEON, ipARGON, ipKRYPTON
                        /*, ipXENON, ipRADON, ipUNUNOCTIUM */ 
                };
                
                long ipFullShell = -1, ipNextFull = 0;
                xValenceDonorDensity = 0.;
                for (long nelem=ipHYDROGEN; nelem < LIMELM; ++nelem)
                {
                        // H -> 1; He -> 2; Li -> 1 (nelem==2,ipFullShell==1), etc.
                        xValenceDonorDensity += 
                                (nelem-ipFullShell)*dense.gas_phase[nelem];
                        if (nelem == ipNoble[ipNextFull])
                        {
                                ipFullShell = nelem;
                                ++ipNextFull;
                        }
                }
                
                //fprintf(ioQQQ,"%g %g\n",dense.eden,xValenceDonorDensity);

                ElectronFraction = (realnum)(MAX2(MIN2(1.0,dense.eden/
                                                                                                                        xValenceDonorDensity),1e-4));
        }
        else
        {
                /* >>chng 03 apr 29, move evaluation of xNeutralParticleDensity to here 
                 * from PresTotCurrent since only used for secondary ionization */
                /* this is total neutral particle density for collisional ionization 
                 * for very high ionization conditions it may be zero */
                realnum xNeutralParticleDensity = 0.;
                for( long nelem=0; nelem < LIMELM; nelem++ )
                {
                        xNeutralParticleDensity += dense.xIonDense[nelem][0];
                }
                
                xNeutralParticleDensity += deut.xIonDense[0];
                
                /* now add all the heavy molecules */
                for( i=0; i < mole_global.num_calc; i++ )
                {
                        /* add in if real molecule and not counted above */
                        if(mole.species[i].location == NULL && mole_global.list[i]->charge == 0 && mole_global.list[i]->parentLabel.empty())
                                xNeutralParticleDensity += (realnum)mole.species[i].den;
                }
                
                {
                        enum {DEBUG_LOC=false};
                        if( DEBUG_LOC )
                        {
                                fprintf(ioQQQ," xIonDense xNeutralParticleDensity tot\t%.3e",xNeutralParticleDensity);
                                for( long nelem=0; nelem < LIMELM; nelem++ )
                                {
                                        fprintf(ioQQQ,"\t%.2e",dense.xIonDense[nelem][0]);
                                }
                                fprintf(ioQQQ,"\n");
                        }
                }
                xValenceDonorDensity = (xNeutralParticleDensity+dense.EdenTrue);
                ElectronFraction = (realnum)(MAX2(MIN2(1.0,dense.EdenTrue/
                                                                                                                        xValenceDonorDensity),1e-4));
        }

        // xBoundValenceDensity must be consistent with ElectronFraction
        // for expressions for ionizations below to have bounded behaviour
        // in the high ElectronFraction limit, i.e. have a factor of (1-EF)
        realnum xBoundValenceDensity = (1.0f-ElectronFraction)*xValenceDonorDensity;

        if( secondaries.lgSecOFF )
        {
                secondaries.HeatEfficPrimary = 1.;
                secondaries.SecIon2PrimaryErg = 0.;
                secondaries.SecExcitLya2PrimaryErg = 0.;
                Cosmic_ray_heat_eff = 0.95;
                Cosmic_ray_sec2prim = 0.05f;
        }
        /* >>chng 03 apr 29, only evaluate one time per zone since drove oscillations
         * in He+ - He0 ionization front in very high Z models, like hizqso */
        else 
        {

                /* this is heating efficiency for high-energy photo ejections.  It is the ratio
                 * of the final heat added to the energy of the photo electron.  Fully
                 * ionized, this is unity, and less than unity for neutral media.  
                 * It is a scale factor that multiplies the
                 * high energy heating rate */
                secondaries.HeatEfficPrimary = 0.9971f*(1.f - pow(1.f - pow(ElectronFraction,(realnum)0.2663f),(realnum)1.3163f));

                /* secondary ionizations per primary Rydberg - the number of secondary 
                 * ionizations produced for each Rydberg of high energy photo-electron 
                 * energy deposited.  It multiplies the high-energy heating rate.  
                 * It is zero for a fully ionized gas and goes to 0.3908 for very neutral gas */
                secondaries.SecIon2PrimaryErg = 0.3908f*pow(1.f - pow(ElectronFraction,(realnum)0.4092f),(realnum)1.7592f);
                /* by dividing by the energy of one Rydberg, converts heating rate 
                 * in ergs into secondary ionization rate */
                secondaries.SecIon2PrimaryErg /= ((realnum)EN1RYD);

                /* This is cosmic ray secondaries per primary (???), 
                 * derived to approximate the curve given in Shull and
                 * van Steenberg for cosmic rays at 35 eV */            
                sec2prim_par_1 = -(1.251f + 195.932f * ElectronFraction);
                sec2prim_par_2 = 1.f + 46.814f * ElectronFraction - 44.969f * 
                        ElectronFraction * ElectronFraction;

                Cosmic_ray_sec2prim = (exp(sec2prim_par_1/SDIV( sec2prim_par_2)));

                /*  number of secondary excitations of L-alpha per erg of high
                 * energy light - actually all Lyman lines 
                 *
                 *  Note--This formula is derived for primary energies greater 
                 *  than 100 eV and is only an approximation.  This will
                 *  over predict the secondary ionization of L-alpha.  We cannot make
                 *  fitting functions for this equation at low energies like we did
                 *  for the heating efficiency and for the number of secondaries
                 *  because the Shull and van Steenberg paper did not publish a similar
                 *  curve for L-alpha */
                secondaries.SecExcitLya2PrimaryErg = 0.4766f*pow(1.f - pow(ElectronFraction,(realnum)0.2735f),(realnum)1.5221f)/((realnum)EN1RYD);

                if( (trace.lgTrace && trace.lgSecIon) )
                {
                        fprintf( ioQQQ, 
                                " csupra H0 %.2e  HeatSum eval sec ion effic, ElectronFraction = %.3e HeatEfficPrimary %.3e SecIon2PrimaryErg %.3e\n", 
                                secondaries.csupra[ipHYDROGEN][0],
                                ElectronFraction,
                                secondaries.HeatEfficPrimary ,
                                secondaries.SecIon2PrimaryErg );
                }

                /* cosmic ray heating, counts as non-ionizing heat since already result of cascade,
                 * this was 35 eV per secondary ionization */
                /* We want to use the heating efficiency that is applicable to a 35 eV
                 * primary electron, the current efficiency used is for 100eV cosmic ray
                 * Here we use the correct value as given in Wolfire et al. 1995 */

                /* In general the equation for the cosmic ray heating rate is:*
                 *                                                                                                                        *
                 *                                                                                                                        *
                 * CR_Heat_Rate = (density)*(cosmic ray ionization rate)*     *
                 *                                (energy of primary electron)*               *
                 *                                (Heating efficiency at that energy)             *
                 *                                                                                                                        *
                 * The product of the last two terms gives the amount of heat *
                 * added by the primary electron, and is dependent upon the   *
                 * electron fraction.  We are using the same average primary  *
                 * electron energy as Wolfire et al. (1995).  We do not,          *
                 * however, use their formula for the heating efficiency.     *
                 * This is because the coefficients (f1, f2, and f3) were     *
                 * originally intended for primary electron energies >100eV.  *
                 * Instead we derived a heating efficiency based on the curves*
                 * given in Shull and van Steenberg (1985).  We interpolated  *
                 * for an energy of 35 eV the heating efficiency for electron *
                 * fractions between 1e-4 and 1                                                           *
                 **************************************************************/

                /*printf("Here is ElectronFraction:\t%.3e\n", ElectronFraction);*/
                Cosmic_ray_heat_eff = - 8.189 - 18.394 * ElectronFraction - 6.608 * ElectronFraction * ElectronFraction * log(ElectronFraction)
                        + 8.322 * exp( ElectronFraction )  + 4.961 * sqrt(ElectronFraction);
        }

        /*******************************************************************
         *
         * get total heating from all species
         *
         *******************************************************************/

        /* get total heating */
        photo_heat_2lev_atoms = 0.;
        photo_heat_ISO_atoms = 0.;
        photo_heat_UTA = 0.;

        /* add in effects of high-energy opacity of CO using C and O atomic opacities
         * k-shell and valence photo of C and O in CO is not explicitly counted elsewhere
         * this trick roughly accounts for it*/
        SaveOxygen1 = dense.xIonDense[ipOXYGEN][0];
        SaveCarbon1 = dense.xIonDense[ipCARBON][0];

        /* atomic C and O will include CO during the heating sum loop */
        fixit(); /* This breaks the invariant for total mass.
                                                *
                                                * In any case, is CO the only species which contributes?
                                                * -- might expect all other molecular species to do so,
                                                * i.e. the item added should perhaps be
                                                * dense.xMolecules[nelem]) -- code duplicated in
                                                * opacity_addtotal
                                                */
        dense.xIonDense[ipOXYGEN][0] += (realnum) findspecieslocal("CO")->den;
        dense.xIonDense[ipCARBON][0] += (realnum) findspecieslocal("CO")->den;

        /* this will hold cooling due to metal collisional ionization */
        CoolHeavy.colmet = 0.;
        /* metals secondary ionization, Lya excitation */
        secmet = 0.;
        smetla = 0.;
        for( ipISO=ipH_LIKE; ipISO<NISO; ++ipISO )
        {
                SeconIoniz_iso[ipISO] = 0.;
                SeconExcit_iso[ipISO] = 0.;
        }

        /* this loop includes hydrogenic, which is special case due to presence
         * of substantial excited state populations */
        for( long nelem=0; nelem<LIMELM; ++nelem)
        {
                secmetsave[nelem] = 0.;
                if( dense.lgElmtOn[nelem] )
                {
                        /* sum heat over all stages of ionization that exist */
                        /* first do the iso sequences,
                         * h-like and he-like are special because full atom always done, 
                         * can be substantial,  pops in excited states, with little in ground 
                         * (true near LTE), these are done in following loop */

                        limit = MIN2( dense.IonHigh[nelem] , nelem+1-NISO );

                        /* loop over all elements/ions done with as two-level systems */
                        for( ion=dense.IonLow[nelem]; ion < limit; ion++ )
                        {
                                /* this will be heating for a single stage of ionization */
                                HeatingLo = 0.;
                                HeatingHi = 0.;
                                for( ns=0; ns < Heavy.nsShells[nelem][ion]; ns++ )
                                {
                                        /* heating by various sub-shells */
                                        HeatingLo += ionbal.PhotoRate_Shell[nelem][ion][ns][1];
                                        HeatingHi += ionbal.PhotoRate_Shell[nelem][ion][ns][2];
                                }

                                /* total photoelectric heating, all shells, for this stage 
                                 * of ionization */
                                thermal.heating[nelem][ion] = dense.xIonDense[nelem][ion]* 
                                        (HeatingLo + HeatingHi*secondaries.HeatEfficPrimary);
                                /* heating due to UTA ionization */
                                photo_heat_UTA += dense.xIonDense[nelem][ion]* 
                                        ionbal.UTA_heat_rate[nelem][ion];

                                /* add to total heating */
                                photo_heat_2lev_atoms += thermal.heating[nelem][ion];
                                /*if( nzone>290 && thermal.heating[nelem][ion]/thermal.htot>0.01 )
                                        fprintf(ioQQQ,"buggg\t%li %li %.3f\n", nelem,ion,thermal.heating[nelem][ion]/thermal.htot);*/

                                /* Cooling due to collisional ionization of heavy elements by thermal electrons
                                 * CollidRate[nelem][ion][1] is cooling, erg/s/atom, eval in ion_collis */
                                CoolHeavy.colmet += dense.xIonDense[nelem][ion]*ionbal.CollIonRate_Ground[nelem][ion][1];

                                /* secondary ionization rate,  */
                                secmetsave[nelem] += HeatingHi*secondaries.SecIon2PrimaryErg* dense.xIonDense[nelem][ion];

                                /* LA excitation rate, =0 if ionized, s-1 cm-3 */
                                smetla += HeatingHi*secondaries.SecExcitLya2PrimaryErg* dense.xIonDense[nelem][ion];
                        }
                        secmet += secmetsave[nelem];

                        /* this branch loop over all ions done with full iso sequence */
                        limit = MAX2( limit, dense.IonLow[nelem] );
                        for( ion=MAX2(0,limit); ion < dense.IonHigh[nelem]; ion++ )
                        {
                                /* this is the iso sequence */
                                ipISO = nelem-ion;
                                /* this will be heating for a single stage of ionization */
                                HeatingLo = 0.;
                                HeatingHi = 0.;
                                /* the outer shell contains the Compton recoil part */
                                for( ns=0; ns < Heavy.nsShells[nelem][ion]; ns++ )
                                {
                                        /* heating, erg s-1 atom-1, by low energy, and then high energy, photons */
                                        HeatingLo += ionbal.PhotoRate_Shell[nelem][ion][ns][1];
                                        HeatingHi += ionbal.PhotoRate_Shell[nelem][ion][ns][2];
                                }

                                /* net heating, erg cm-3 s-1 */
                                thermal.heating[nelem][ion] = iso_sp[ipISO][nelem].st[0].Pop()*
                                        (HeatingLo + HeatingHi*secondaries.HeatEfficPrimary);

                                /* heating due to UTA ionization, erg cm-3 s-1 */
                                photo_heat_UTA += dense.xIonDense[nelem][ion]* 
                                        ionbal.UTA_heat_rate[nelem][ion];

                                /* add to total heating */
                                photo_heat_ISO_atoms += thermal.heating[nelem][ion];

                                if( secondaries.SecIon2PrimaryErg > SMALLFLOAT && xBoundValenceDensity > SMALLFLOAT )
                                {
                                        /* prevent crash in very high ionization conditions 
                                         * where xBoundValenceDensity is zero */
                                        /* secondary ionization rate,  */
                                        SeconIoniz_iso[ipISO] += HeatingHi*secondaries.SecIon2PrimaryErg* 
                                                iso_sp[ipISO][nelem].st[0].Pop()/
                                                xBoundValenceDensity;

                                        /* LA excitation rate, =0 if ionized, units excitations s-1 */
                                        SeconExcit_iso[ipISO] += HeatingHi*secondaries.SecExcitLya2PrimaryErg* 
                                                iso_sp[ipISO][nelem].st[0].Pop()/
                                                xBoundValenceDensity;

                                        ASSERT( SeconIoniz_iso[ipISO]>=0. && 
                                                SeconExcit_iso[ipISO]>=0.);
                                }
                        }

                        /* make sure stages of ionization with no abundances,
                         * also has no heating */
                        for( ion=0; ion<dense.IonLow[nelem]; ion++ )
                        {
                                ASSERT( thermal.heating[nelem][ion] == 0. );
                        }
                        for( ion=dense.IonHigh[nelem]+1; ion<nelem+1; ion++ )
                        {
                                ASSERT( thermal.heating[nelem][ion] == 0. );
                        }
                }
        }
        if( trace.lgTrace && trace.lgSecIon )
        {
                double savemax=0.;
                long int ipsavemax=-1;
                for( long nelem=ipHYDROGEN; nelem<LIMELM; ++nelem )
                {
                        if( secmetsave[nelem] > savemax )
                        {
                                savemax = secmetsave[nelem];
                                ipsavemax = nelem;
                        }
                }
                fprintf( ioQQQ, 
                        "   HeatSum secmet largest contributor element %li frac of total %.3e, total %.3e\n", 
                        ipsavemax,
                        savemax/SDIV(secmet),
                        secmet);
        }

        /* now reset the abundances */
        dense.xIonDense[ipOXYGEN][0] = SaveOxygen1;
        dense.xIonDense[ipCARBON][0] = SaveCarbon1;

        /* convert secmet to proper final units */
        /*fprintf(ioQQQ,"bugggg\t%li\t%.3e\t%.3e\t%.3e\n", nzone , 
                secmet , xBoundValenceDensity , secmet / xBoundValenceDensity );*/
        /* prevent crash when xBoundValenceDensity is zero */
        if( secondaries.SecIon2PrimaryErg > SMALLFLOAT && xBoundValenceDensity > SMALLFLOAT )
        {
                /* convert from s-1 cm-3 to s-1 - a true rate */
                secmet /= xBoundValenceDensity;
                smetla /= xBoundValenceDensity;
        }
        else
        {
                /* zero */
                secmet = 0.;
                smetla = 0.;
        }

        /* >>chng 01 dec 20, do full some over all secondaries */
        /* bound Compton recoil heating */
        /* >>chng 02 mar 28, save heating in this var rather than heating[0][18] 
         * since now saved in photo heat 
         * this is only used for a printout and in lines, not as heat since already counted*/
        ionbal.CompRecoilHeatLocal = 0.;
        for( long nelem=0; nelem<LIMELM; ++nelem )
        {
                for( ion=0; ion<nelem+1; ++ion )
                {
                        ionbal.CompRecoilHeatLocal += 
                                ionbal.CompRecoilHeatRate[nelem][ion]*secondaries.HeatEfficPrimary*dense.xIonDense[nelem][ion];
                }
        }
        /* >>chng 05 nov 26, include this term - bound ionization of H2 
         * assume total cs is that of two separated H */
        ionbal.CompRecoilHeatLocal += 
                2.*ionbal.CompRecoilHeatRate[ipHYDROGEN][0]*secondaries.HeatEfficPrimary*hmi.H2_total;

        /* find heating due to charge transfer 
         * >>chng 05 oct 29, move from here to conv base so that can be treated as cooling if 
         * negative heating */
        thermal.heating[0][24] = thermal.char_tran_heat;

        /* heating due to pair production */
        thermal.heating[0][21] = 
                ionbal.PairProducPhotoRate[2]*secondaries.HeatEfficPrimary*(dense.gas_phase[ipHYDROGEN] + 4.F*dense.gas_phase[ipHELIUM]);
        /* last term above is number of nuclei in helium */

        /* this is heating due to fast neutrons, assumed to secondary ionize */
        thermal.heating[0][20] = 
                ionbal.xNeutronHeatRate*secondaries.HeatEfficPrimary*dense.gas_phase[ipHYDROGEN];

        /* turbulent heating, assumed to be a non-ionizing heat agent, added here */
        thermal.heating[0][20] += ionbal.ExtraHeatRate;

        /* UTA heating */
        thermal.heating[0][7] = photo_heat_UTA;
        /*fprintf(ioQQQ,"DEBUG UTA heat %.3e\n", photo_heat_UTA/SDIV(thermal.htot ));*/

        // diatomic photoionization heating 
        thermal.heating[0][18] = 0.;
        for( diatom_iter diatom = diatoms.begin(); diatom != diatoms.end(); ++diatom )
        {
                /*>>KEYWORD     H2 photoionization heating */
                thermal.heating[0][18] += (*diatom)->Abund() *
                        ( (*diatom)->photo_heat_soft + (*diatom)->photo_heat_hard*secondaries.HeatEfficPrimary);
        }
        /* >>chng 05 nov 27, approximate heating due to H2+, H3+ photoionization
         * assuming H0 rates */
        /*>>KEYWORD     H2+ photoionization heating; H3+ photoionization heating */
        thermal.heating[0][26] = (findspecieslocal("H2+")->den+findspecieslocal("H3+")->den) *
                (ionbal.PhotoRate_Shell[ipHYDROGEN][0][0][1] + 
                ionbal.PhotoRate_Shell[ipHYDROGEN][0][0][2]*secondaries.HeatEfficPrimary);

        /* add on cosmic rays - most important in neutral or molecular gas, use
         * difference between total H and H+ density as substitute for sum of
         * H in atoms and all molecules, but only in limit where difference is
         * significant */
#       if 0
        double hneut;
        if( (dense.gas_phase[ipHYDROGEN] - dense.xIonDense[ipHYDROGEN][1])/
                dense.gas_phase[ipHYDROGEN]<0.001 )
        {
                /* limit where most H is ionized - simply use atomic and H2 */
                hneut = dense.xIonDense[ipHYDROGEN][0] + 2.*(findspecieslocal("H2")->den+findspecieslocal("H2*")->den);
        }
        else
        {
                /* limit where neutral is significant, use different between total and H+ */
                hneut = dense.gas_phase[ipHYDROGEN] - dense.xIonDense[ipHYDROGEN][1];
        }
#       endif

        /* cosmic ray heating */
        thermal.heating[1][6] = 
                ionbal.CosRayHeatNeutralParticles*
                xBoundValenceDensity * Cosmic_ray_heat_eff;
        /* cosmic ray heating of thermal electrons */
        /* >>refer      CR      physics Ferland, G.J. & Mushotzky, R.F., 1984, ApJ, 286, 42 */
        thermal.heating[1][6] += ionbal.CosRayHeatThermalElectrons * dense.eden;

        /* now sum up all heating agents not included in sum over normal bound levels above */
        OtherHeat = 0.;
        for( long nelem=0; nelem<LIMELM; ++nelem)
        {
                /* we now have ionization solution for this element,sum heat over
                 * all stages of ionization that exist */
                /* >>>chng 99 may 08, following loop had started at nelem+3, and so missed [1][0],
                 * which is excited states of hydrogenic species.  increase this limit */
                for( i=nelem+1; i < LIMELM; i++ )
                {
                        OtherHeat += thermal.heating[nelem][i];
                }
        }

        thermal.htot = OtherHeat + photo_heat_2lev_atoms + photo_heat_ISO_atoms;

        /* following checks whether total heating is strange, if we are not in search phase */
        if( called.lgTalk && !conv.lgSearch )
        {
                /* print this warning if not constant temperature and neg heat */
                if( thermal.htot < 0. && !thermal.lgTemperatureConstant)
                {
                        fprintf( ioQQQ, 
                                " Total heating is <0; is this model collisionally ionized? zone is %li\n",
                                nzone );
                }
                else if( thermal.htot == 0. )
                {
                        fprintf( ioQQQ, 
                                " Total heating is 0; is the density small? zone is %li\n",
                                nzone);
                }
        }

        /* add on line heating to this array, heatl was evaluated in sumcool
         * not zero, because of roundoff error */
        if( thermal.heatl/thermal.ctot < -1e-15 )
        {
                fprintf( ioQQQ, " HeatSum gets negative line heating,%10.2e%10.2e this is insane.\n", 
                  thermal.heatl, thermal.ctot );

                fprintf( ioQQQ, " this is zone%4ld\n", nzone );
                ShowMe();
                cdEXIT(EXIT_FAILURE);
        }

        fixit(); // much or all of this secondary stuff (next ~120 lines) should be updated much earlier
                // solvers in conv_base use outdated details

        /*******************************************************************
         *
         * secondary ionization and excitation rates 
         *
         *******************************************************************/

        /* the terms cosmic_ray_ionization_rate & SecExcitLyaRate contain energies added in highen.  
         * The only significant one is usually bound Compton heating except when 
         * cosmic rays are present */

        if( secondaries.SecIon2PrimaryErg > SMALLFLOAT && xBoundValenceDensity > SMALLFLOAT )
        {
                /* add on ionization rate s-1 cm-3 due to pair production */
                /* next two terms account for secondary ionization and excitation due to pair productions.
                 * The code integrates over the radiation field where \gamma <-> e- e+ is possible -
                 * that is ionbal.PairProducPhotoRate.  For all SEDs of realistic sources (AGN, or x-ray binaries)
                 * the radiation field over this range is small compared with the FUV/x-ray.  Pair production will,
                 * as a result, only be important energetically in well-shielded regions where much of the SED
                 * is absorbed.  In these regions gas would be neutral or molecular and the pair would produce
                 * the same effects as a cosmic ray - heating, excitation, and ionization.  That is why the code is
                 * here. Given the shape of the SED these effects are the largest pair production should produce -
                 * even then it is negligible.
                 */

                /* the photon rates in ionbal.PairProducPhotoRate are the integral over the range that the
                 * do pair production using cross sections from Figure 41 of Experimental Nuclear Physics,
                 * Vol1, E.Segre, ed
                 * factor of four in DensityRatio accounts for additional nucleons in alpha particle */
                realnum DensityRatio = (dense.gas_phase[ipHYDROGEN] + 
                        4.F*dense.gas_phase[ipHELIUM])/xBoundValenceDensity;

                pair_production_ionization_rate = 
                        ionbal.PairProducPhotoRate[2]*secondaries.SecIon2PrimaryErg*DensityRatio;

                /* total secondary excitation rate cm-3 s-1 for Lya due to pair production*/
                SecExcitLyaRate = 
                        ionbal.PairProducPhotoRate[2]*secondaries.SecExcitLya2PrimaryErg*1.3333*DensityRatio;

                /* ionization rate of fast neutrons */
                fast_neutron_ionization_rate = 
                        ionbal.xNeutronHeatRate*secondaries.SecIon2PrimaryErg*DensityRatio;

                /* Secondary excitation rate due to neutrons */
                SecExcitLyaRate += 
                        ionbal.xNeutronHeatRate*secondaries.SecExcitLya2PrimaryErg*1.3333*DensityRatio;

                /* cosmic ray Lya excitation rate */
                SecExcitLyaRate += 
                        /* multiply by atomic H and He densities */
                        ionbal.CosRayHeatNeutralParticles*secondaries.SecExcitLya2PrimaryErg*1.3333*DensityRatio;
        }
        else
        {
                /* zero */
                pair_production_ionization_rate = 0.;
                SecExcitLyaRate = 0.;
                fast_neutron_ionization_rate = 0.;
        }

        /* cosmic ray ionization */
        /* >>>chng 99 apr 29, term in PhotoRate was not present */
        cosmic_ray_ionization_rate = 
                /* this term is H^0 cosmic ray ionization, set in highen, did not multiply by
                 * collider density in highen, so do not divide by it here */
                /* >>chng 99 jun 29, added SecIon2PrimaryErg to cosmic ray rate, also multiply
                 * by number of secondaries per primary*/
                ionbal.CosRayIonRate*Cosmic_ray_sec2prim +
                /* this is the cosmic ray heating rate */
                ionbal.CosRayHeatNeutralParticles*secondaries.SecIon2PrimaryErg;

        /* find total suprathermal collisional ionization rate
         * CSUPRA is H0 col ionize rate from non-thermal electrons (inverse sec)
         * x12tot is LA excitation rate, units s-1
         * SECCMP evaluated in HIGHEN, =ioniz rate for cosmic rays, sec bound */

        /* option to force secondary ionization rate, normally false */
        if( secondaries.lgCSetOn )
        {
                for( long nelem=ipHYDROGEN; nelem<LIMELM; ++nelem )
                {
                        for( ion=0; ion<nelem+1; ++ion )
                        {
                                secondaries.csupra[nelem][ion] = secondaries.SetCsupra*secondaries.csupra_effic[nelem][ion];
                        }
                }
                secondaries.x12tot = secondaries.SetCsupra;
        }
        else
        {
                double csupra = cosmic_ray_ionization_rate + 
                        pair_production_ionization_rate +
                        fast_neutron_ionization_rate +
                        SeconIoniz_iso[ipH_LIKE] + 
                        SeconIoniz_iso[ipHE_LIKE] + 
                        secmet;

                /* now fill in ionization rates for all elements and ion stages */
                for( long nelem=ipHYDROGEN; nelem<LIMELM; ++nelem )
                {
                        for( ion=0; ion<nelem+1; ++ion )
                        {
                                secondaries.csupra[nelem][ion] = (realnum)csupra*secondaries.csupra_effic[nelem][ion];
                        }
                }

                fixit(); // why does x12tot include non Ly-a stuff here, and get used to scale other lines elsewhere?
                /* secondary suprathermal excitation of Ly-alpha, excitations s-1 */
                secondaries.x12tot = SecExcitLyaRate + 
                        SeconExcit_iso[ipH_LIKE] + 
                        SeconExcit_iso[ipHE_LIKE] + 
                        smetla;

                if (0)
                        fprintf(ioQQQ,"x12 %ld %15.8g %15.8g %15.8g\n",nzone,
                                          secondaries.x12tot,
                                          secondaries.SecExcitLya2PrimaryErg,ElectronFraction);
        }

        if( trace.lgTrace && secondaries.csupra[ipHYDROGEN][0] > 0. )
        {
                fprintf( ioQQQ, 
                        "   HeatSum return CSUPRA %9.2e SECCMP %6.3f SecHI %6.3f SECHE %6.3f SECMET %6.3f efrac= %9.2e \n", 
                  secondaries.csupra[ipHYDROGEN][0], 
                  (cosmic_ray_ionization_rate+pair_production_ionization_rate+fast_neutron_ionization_rate)/secondaries.csupra[ipHYDROGEN][0], 
                  SeconIoniz_iso[ipH_LIKE] / secondaries.csupra[ipHYDROGEN][0], 
                  SeconIoniz_iso[ipHE_LIKE]/secondaries.csupra[ipHYDROGEN][0], 
                  secmet/secondaries.csupra[ipHYDROGEN][0] ,
                  ElectronFraction );
        }

        /*******************************************************************
         *
         * get derivative of total heating
         *
         *******************************************************************/

        /* now get derivative of heating due to photoionization, 
         * >>chng 96 jan 14
         *>>>>>NB heating decreasing with increasing temp is negative dH/dT */
        thermal.dHeatdT = -0.7*(photo_heat_2lev_atoms+photo_heat_ISO_atoms+
                photo_heat_UTA)/phycon.te;
        /* >>chng 04 feb 28, add this correction factor - when gas totally neutral heating
         * does not depend on temperature - when ionized depends on recom coefficient - this
         * smoothly joins two limits */
        thermal.dHeatdT *= dense.xIonDense[ipHYDROGEN][1]/dense.gas_phase[ipHYDROGEN];
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  0 %.3e  %.3e  %.3e \n", 
                thermal.dHeatdT,
                photo_heat_2lev_atoms,
                photo_heat_ISO_atoms);

        /* oldfac was factor used in old implementation
         * any term using it should be rethought */
        oldfac = -0.7/phycon.te;

        /* carbon monoxide */
        thermal.dHeatdT += thermal.heating[0][9]*oldfac;

        /* Ly alpha collisional heating */
        thermal.dHeatdT += thermal.heating[0][10]*oldfac;

        /* line heating */
        thermal.dHeatdT += thermal.heating[0][22]*oldfac;
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  1 %.3e \n", thermal.dHeatdT);

        /* free free heating, propto T^-0.5
         * >>chng 96 oct 30, from heating(1,12) to CoolHeavy.brems_heat_total,
         * do cooling separately assume CoolHeavy.brems_heat_total goes as T^-3/2
         * dHTotDT = dHTotDT + heating(1,12) * (-0.5/te) */
        thermal.dHeatdT += CoolHeavy.brems_heat_total*(-1.5/phycon.te);

        /* >>chng 04 aug 07, use better estimate for heating derivative; needed in PDRs, PvH */
        /* this includes PE, thermionic, and collisional heating of the gas by the grains */
        thermal.dHeatdT += gv.dHeatdT;

        /* helium triplets heating */
        thermal.dHeatdT += thermal.heating[1][2]*oldfac;
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  2 %.3e \n", thermal.dHeatdT);

        /* hydrogen molecule collisional deexcitation heating */
        /* >>chng 04 jan 25, add max to prevent cooling from entering here */
        /*thermal.dHeatdT += MAX2(0.,thermal.heating[0][8])*oldfac;*/
        if( hmi.HeatH2Dexc_used > 0. )
                thermal.dHeatdT += hmi.deriv_HeatH2Dexc_used;

        /* >>chng 96 nov 15, had been oldfac below, wrong sign
         * H- H minus heating, goes up with temp since rad assoc does */
        thermal.dHeatdT += thermal.heating[0][15]*0.7/phycon.te;

        /* H2+ heating */
        thermal.dHeatdT += thermal.heating[0][16]*oldfac;

        /* Balmer continuum and all other excited states
         * - T goes up so does pop and heating
         * but this all screwed up by change in eden */
        thermal.dHeatdT += thermal.heating[0][1]*oldfac;
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  3 %.3e \n", thermal.dHeatdT);

        /* all three body heating, opposite of coll ion cooling */
        thermal.dHeatdT += thermal.heating[0][3]*oldfac;

        /* bound electron recoil heating
        thermal.dHeatdT += ionbal.CompRecoilHeatLocal*oldfac; */

        /* Compton heating */
        thermal.dHeatdT += thermal.heating[0][19]*oldfac;

        /* extra heating source, usually zero */
        thermal.dHeatdT += thermal.heating[0][20]*oldfac;

        /* pair production */
        thermal.dHeatdT += thermal.heating[0][21]*oldfac;
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  4 %.3e \n", thermal.dHeatdT);

        /* derivative of heating due to collisions of H lines, heating(1,24) */
        for( ipISO=ipH_LIKE; ipISO<NISO; ++ipISO )
        {
                for( long nelem=ipISO; nelem<LIMELM; ++nelem)
                {
                        thermal.dHeatdT += iso_sp[ipISO][nelem].dLTot;
                }
        }

        /* heating due to large FeII atom, zero unless atom FeII is entered,
         * FeII.Fe2_large_heat was entered into thermal.heating[25][27] */
        if( FeII.Fe2_large_heat > 0.  )
        {
                thermal.dHeatdT += FeII.ddT_Fe2_large_cool;
        }
        if( PRT_DERIV )
                fprintf(ioQQQ,"DEBUG dhdt  5 %.3e \n", thermal.dHeatdT);

        /* possibility of getting empirical heating derivative
         * normally false, set true with 'set numerical derivatives' command */
        if( NumDeriv.lgNumDeriv )
        {
                if( ((nzone > 2 && nzone == nzSave) && 
                     ! fp_equal( oldtemp, phycon.te )) && nhit > 4 )
                {
                        /* hnit is number of tries on this zone - use to stop numerical problems
                         * do not evaluate numerical derivative until well into solution */
                        deriv = (oldheat - thermal.htot)/(oldtemp - phycon.te);
                        thermal.dHeatdT = deriv;
                }
                else
                {
                        deriv = thermal.dHeatdT;
                }

                /* this happens when new zone starts */
                if( nzone != nzSave )
                {
                        nhit = 0;
                }
                nzSave = nzone;
                nhit += 1;
                oldheat = thermal.htot;
                oldtemp = phycon.te;
        }

        if( trace.lgTrace && trace.lgHeatBug )
        {
                ipnt = 0;
                /* this loops through the 2D array that contains all agents counted in htot */
                for( i=0; i < LIMELM; i++ )
                {
                        for( j=0; j < LIMELM; j++ )
                        {
                                if( thermal.heating[i][j]/thermal.htot > FAINT_HEAT )
                                {
                                        ipsave[ipnt] = i;
                                        jpsave[ipnt] = j;
                                        save[ipnt] = thermal.heating[i][j]/thermal.htot;
                                        /* increment ipnt, but do not let it get too big */
                                        ipnt = MIN2((long)NDIM-1,ipnt+1);
                                }
                        }
                }

                /* now check for possible line heating not counted in 1,23
                 * there should not be any significant heating source here
                 * since they would not be counted in derivative correctly */
                for( i=0; i < thermal.ncltot; i++ )
                {
                        if( thermal.heatnt[i]/thermal.htot > FAINT_HEAT )
                        {
                                ipsave[ipnt] = -1;
                                jpsave[ipnt] = i;
                                save[ipnt] = thermal.heatnt[i]/thermal.htot;
                                ipnt = MIN2((long)NDIM-1,ipnt+1);
                        }
                }

                fprintf( ioQQQ, 
                  "    HeatSum HTOT %.3e Te:%.3e dH/dT%.2e other %.2e photo 2lev %.2e photo iso %.2e\n", 
                  thermal.htot, 
                  phycon.te, 
                  thermal.dHeatdT ,
                  /* total heating is sum of following three terms
                   * OtherHeat is a sum over all other heating agents */
                  OtherHeat , 
                  photo_heat_2lev_atoms, 
                  photo_heat_ISO_atoms);

                fprintf( ioQQQ, "  " );
                for( i=0; i < ipnt; i++ )
                {
                        /*lint -e644 these three are initialized above */
                        fprintf( ioQQQ, "   [%ld][%ld]%6.3f",
                                ipsave[i], 
                                jpsave[i],
                                save[i] );
                        /*lint +e644 these three are initialized above */
                        /* throw a cr every n numbers */
                        if( !(i%8) && i>0 && i!=(ipnt-1) )
                        {
                                fprintf( ioQQQ, "\n  " );
                        }
                }
                fprintf( ioQQQ, "\n" );
        }
        return;
}

/* =============================================================================*/
/* HeatZero is called by ConvBase */
void HeatZero( void )
{
        long int i , j;

        DEBUG_ENTRY( "HeatZero()" );

        for( i=0; i < LIMELM; i++ )
        {
                for( j=0; j < LIMELM; j++ )
                {
                        thermal.heating[i][j] = 0.;
                }
        }
        return;
}

---