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/* This file is part of Cloudy and is copyright (C)1978-2013 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */
/*HCSAR_interp interpolate on collision strengths */
/*C6cs123 line collision rates for lower levels of hydrogenic carbon, n=1,2,3 */
/*Ca20cs123 line collision rates for lower levels of hydrogenic calcium, n=1,2,3 */
/*Hydcs123 Hydrogenic de-excitation collision rates n=1,2,3 */
/*H1cs123 hydrogen collision data levels involving 1s,2s,2p,3. */
/*Ne10cs123 line collision rates for lower levels of hydrogenic neon, n=1,2,3 */
/*He2cs123 line collision strengths for lower levels of helium ion, n=1,2,3, by K Korista */
/*Fe26cs123 line collision rates for lower levels of hydrogenic iron, n=1,2,3 */
#include "cddefines.h"
#include "atmdat.h"
#include "dense.h"
#include "helike_cs.h"
#include "hydro_vs_rates.h"
#include "iso.h"
#include "opacity.h"
#include "phycon.h"
#include "physconst.h"
#include "taulines.h"

STATIC double Fe26cs123(long int i, long int j);
STATIC double He2cs123(long int i, long int j);
STATIC double Hydcs123(long int ilow, long int ihigh, long int iz, long int chType);
STATIC double C6cs123(long int i, long int j);
STATIC double Ca20cs123(long int i, long int j);
STATIC double Ne10cs123(long int i, long int j);

STATIC realnum HCSAR_interp( int ipLo , int ipHi );
STATIC double CS_ThermAve_PR78(long ipISO, long nelem, long nHi, long nLo, double deltaE, double temp );
STATIC double Therm_ave_coll_str_int_PR78( double EOverKT );
STATIC double CS_PercivalRichards78( double Ebar );

static long global_ipISO, global_nelem, global_nHi, global_nLo;
static double kTRyd, global_deltaE;

static const realnum HCSTE[NHCSTE] = {5802.f,11604.f,34812.f,58020.f,116040.f,174060.f,232080.f,290100.f};

/*HCSAR_interp interpolate on collision strengths */
STATIC realnum HCSAR_interp( int ipLo , int ipHi )
{

        static int ip=1;
        realnum cs;

        DEBUG_ENTRY( "HCSAR_interp()" );

        if( ipLo==1 && ipHi==2 )
        {
                fprintf(ioQQQ,"HCSAR_interp was called for the 2s-2p transition, which it cannot do\n");
                cdEXIT(EXIT_FAILURE);
        }
        if( phycon.te <= HCSTE[0] )
        {
                cs = t_ADfA::Inst().h_coll_str( ipLo , ipHi , 0 );
        }
        else if( phycon.te >= HCSTE[NHCSTE-1] )
        {
                cs = t_ADfA::Inst().h_coll_str( ipLo , ipHi , NHCSTE-1 );
        }
        else
        {
                /* the ip index is most likely correct since it points to the last temperature */
                if( (HCSTE[ip-1] >= phycon.te ) || ( phycon.te > HCSTE[ip]) )
                {
                        /* we must find the temperature in the array */
                        for( ip=1; ip<NHCSTE; ++ip )
                        {
                                if( (HCSTE[ip-1] < phycon.te ) && ( phycon.te <= HCSTE[ip]) )
                                        break;
                        }
                }
                /* we now have the index */
                cs = t_ADfA::Inst().h_coll_str( ipLo , ipHi , ip-1 ) + 
                        (t_ADfA::Inst().h_coll_str( ipLo , ipHi , ip ) - t_ADfA::Inst().h_coll_str( ipLo , ipHi , ip-1 ) ) / (HCSTE[ip]-HCSTE[ip-1] ) *
                        ((realnum)phycon.te - HCSTE[ip-1] );
                if( cs <= 0.)
                {
                        fprintf(ioQQQ," insane cs returned by HCSAR_interp, values are\n");
                        fprintf(ioQQQ,"%.3f %.3f \n", t_ADfA::Inst().h_coll_str( ipLo , ipHi , ip-1 ),t_ADfA::Inst().h_coll_str( ipLo , ipHi , ip ) );
                }
        }
        return(cs);
}

/*Hydcs123 Hydrogenic de-excitation collision strengths between levels n=1,2,3,
 * for any charge.  routine only called by HydroCSInterp to fill in hydroline arrays
 * with collision strengths */
STATIC double Hydcs123(
         /* lower principal quantum number, 1, 2, or 3, in this routine 
          * 1 is 1s, 2 is 2s, 3 is 2p, and 4 is 3s, 5 is 3p, and 6 is 3d */
         long int ipLow, 
         /* upper principal quantum nubmer, 2, 3, or 4 */
         long int ipHi, 
         /* charge, 0 for hydrogen, 1 for helium, etc */
         long int nelem, 
         /* = 'e' for electron collisions, ='p' for proton */
         long int chType)
{
        long int i,
          j, 
          k;
        double C, 
          D, 
          EE, 
          expq ,
          Hydcs123_v, 
          Ratehigh, 
          Ratelow, 
          TeUse, 
          gLo, 
          gHi, 
          q, 
          rate, 
          slope, 
          temp, 
          temphigh, 
          templow, 
          tev, 
          x, 
          QuanNLo, 
          QuanNUp, 
          Charge, 
          ChargeSquared, 
          zhigh, 
          zlow;
        static const double ap[5] = {-2113.113,729.0084,1055.397,854.632,938.9912};
        static const double bp[5] = {-6783.515,-377.7190,724.1936,493.1107,735.7466}; 
        static const double cp[5] = {-3049.719,226.2320,637.8630,388.5465,554.6369};
        static const double dp[5] = {3514.5153,88.60169,-470.4055,-329.4914,-450.8459};
        static const double ep[5] = {0.005251557,0.009059154,0.008725781,0.009952418,0.01098687};
        static const double ae[5] = {-767.5859,-643.1189,-461.6836,-429.0543,-406.5285};
        static const double be[5] = {-1731.9178,-1442.548,-1055.364,-980.3079,-930.9266};
        static const double ce[5] = {-939.1834,-789.9569,-569.1451,-530.1974,-502.0939};
        static const double de[5] = {927.4773,773.2008,564.3272,524.2944,497.7763};
        static const double ee[5] = {-0.002528027,-0.003793665,-0.002122103,-0.002234207,-0.002317720};
        static const double A[2] = {4.4394,0.0};
        static const double B[2] = {0.8949,0.8879};
        static const double C0[2] = {-0.6012,-0.2474};
        static const double C1[2] = {-3.9710,-3.7562};
        static const double C2[2] = {-4.2176,2.0491};
        static const double D0[2] = {2.930,0.0539};
        static const double D1[2] = {1.7990,3.4009};
        static const double D2[2] = {4.9347,-1.7770};

        DEBUG_ENTRY( "Hydcs123()" );
        /* Hydrogenic de-excitation collision rates n=1,2,3 
         * >>refer      h1      cs      Callaway, J. 1983, Phys Let A, 96, 83
         * >>refer      h1      cs      Zygelman, B., & Dalgarno, A. 1987, Phys Rev A, 35, 4085 
         * for 2p-2s only.
         * The fit from Callaway is in nuclear charge for 1s - 2s,2p only.
         * For transtions involving level 3, interpolation in Z involving
         * the functions He2cs123,C6cs123,Ne10cs123,Ca20cs123, Fe26cs123.
         *
         * The fits from ZD are for 2p-2s for Z=2,6,12,16,18 only other charges are
         * interpolated, both electron and proton rates are included,
         * the variable chType is either 'e' or 'p'.
         *
         * ipLow is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         * ipHi is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d) */

        /* for Callaway fit: */
        /* for Zygelman and Dalgarno: */

        /* first entry is 2p, then 2s */

        /* fit in nuclear charge Z for 2p-2s collisions in hydrogenic species
         * equation is a+bx+cx^2ln(x)+dexp(x)+eln(x)/x^2, where x=te/Z^2 in a.u.
         * first are the proton rates: */
        /* these are electron rates: */

        /* following is for charged species */
        /* charge is on scale with He+=1, Li++=2, etc */
        ASSERT( nelem > ipHYDROGEN );
        ASSERT( nelem < LIMELM );

        /* these are the pointers to upper and lower levels.  1=1s, 2=2s, 3=2p, 4=3 */
        ASSERT( ipLow > 0);
        ASSERT( ipLow <= 3);
        ASSERT( ipHi > 1 );
        ASSERT( ipHi <=6 );

        /* set quantum numbers and stat. weights of the transitions: */
        if( ipHi == 6 )
        {
                /* upper is n=3 then set level, stat. weight */
                QuanNUp = 3.;
                gHi = 10.;
                /* following will be set here even though it is not used in this case,
                 * to prevent good compilers from falsing on i not set,
                 * there is assert when used to make sure it is ok */
                i = -1;
        }
        else if( ipHi == 5 )
        {
                /* upper is n=3 then set level, stat. weight */
                QuanNUp = 3.;
                gHi = 6.;
                /* following will be set here even though it is not used in this case,
                 * to prevent good compilers from falsing on i not set,
                 * there is assert when used to make sure it is ok */
                i = -1;
        }
        else if( ipHi == 4 )
        {
                /* upper is n=3 then set level, stat. weight */
                QuanNUp = 3.;
                gHi = 2.;
                /* following will be set here even though it is not used in this case,
                 * to prevent good compilers from falsing on i not set,
                 * there is assert when used to make sure it is ok */
                i = -1;
        }
        else if( ipHi == 3 )
        {
                /* upper is nl=2p then set level, stat. weight */
                QuanNUp = 2.;
                gHi = 6.;
                /* used to point within vectors defined above */
                i = 0;
        }
        else if( ipHi == 2 )
        {
                /* upper is nl=2s then set level, stat. weight */
                QuanNUp = 2.;
                gHi = 2.;
                /* used to point within vectors defined above */
                i = 1;
        }
        else
        {
                fprintf( ioQQQ, " Insane levels in Hydcs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        /* which lower level? */
        if( ipLow == 1 )
        {
                /* lower is n=1 then set level, stat. weight */
                QuanNLo = 1.;
                gLo = 2.;
        }
        else if( ipLow == 2 )
        {
                /* lower is nl=2s then set level, stat. weight */
                QuanNLo = 2.;
                gLo = 2.;
        }
        else if( ipLow == 3 )
        {
                QuanNLo = 2.;
                gLo = 6.;
        }
        else
        {
                fprintf( ioQQQ, " Insane levels in Hydcs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        /* following is the physical charge */
        Charge = (double)(nelem + 1);
        /* square of charge */
        ChargeSquared = Charge*Charge;

        if( ipLow == 2 && ipHi == 3 )
        {
                /*************************************** this is 2p-2s:
                 * series of if statements determines which entries Charge is between. */
                if( nelem < 1 )
                {
                        /* this can't happen since routine returned above when ip=1 and 
                         * special atomic hydrogen routine called */
                        fprintf( ioQQQ, " insane charge given to Hydcs123\n" );
                        cdEXIT(EXIT_FAILURE);
                }
                else if( nelem == 1 )
                {
                        zlow = 2.;
                        j = 1;
                        zhigh = 2.;
                        k = 1;
                }
                /* Li through C */
                else if( nelem <= 5 )
                {
                        zlow = 2.;
                        j = 1;
                        zhigh = 6.;
                        k = 2;
                }
                else if( nelem <= 11 )
                {
                        zlow = 6.;
                        j = 2;
                        zhigh = 12.;
                        k = 3;
                }
                else if( nelem <= 15 )
                {
                        zlow = 12.;
                        j = 3;
                        zhigh = 16.;
                        k = 4;
                }
                else if( nelem <= 17 )
                {
                        zlow = 16.;
                        j = 4;
                        zhigh = 18.;
                        k = 5;
                }
                /* following changed to else from else if, 
                 * to prevent false comment in good compilers */
                /*else if( nelem > 18 )*/
                else 
                {
                        zlow = 18.;
                        j = 5;
                        zhigh = 18.;
                        k = 5;
                }

                /* convert Te to a.u./Z^2
                 * determine rate at the low Charge */
                x = EVRYD/TE1RYD*phycon.te/(27.211396*pow2(zlow));
                TeUse = MIN2(x,0.80);
                x = MAX2(0.025,TeUse);

                /* what type of collision are we dealing with? */
                if( chType == 'e' )
                {
                        /* electron collisions */
                        Ratelow = ae[j-1] + be[j-1]*x + ce[j-1]*pow2(x)*log(x) + de[j-1]*
                          exp(x) + ee[j-1]*log(x)/pow2(x);
                }
                else if( chType == 'p' )
                {
                        Ratelow = ap[j-1] + bp[j-1]*x + cp[j-1]*pow2(x)*log(x) + dp[j-1]*
                          exp(x) + ep[j-1]*log(x)/pow2(x);
                }
                else 
                {
                        /* this can't happen */
                        fprintf( ioQQQ, " insane collision species given to Hydcs123\n" );
                        cdEXIT(EXIT_FAILURE);
                }

                /* determine rate at the high Charge */
                x = EVRYD/TE1RYD*phycon.te/(27.211396*pow2(zhigh));
                TeUse = MIN2(x,0.80);
                x = MAX2(0.025,TeUse);
                if( chType == 'e' )
                {
                        Ratehigh = ae[k-1] + be[k-1]*x + ce[k-1]*pow2(x)*log(x) + 
                          de[k-1]*exp(x) + ee[k-1]*log(x)/pow2(x);
                }
                else
                {
                        Ratehigh = ap[k-1] + bp[k-1]*x + cp[k-1]*pow2(x)*log(x) + 
                          dp[k-1]*exp(x) + ep[k-1]*log(x)/pow2(x);
                }
                /* linearly interpolate in charge */
                if( fp_equal( zlow, zhigh ) )
                {
                        rate = Ratelow;
                }
                else
                {
                        slope = (Ratehigh - Ratelow)/(zhigh - zlow);
                        rate = slope*(Charge - zlow) + Ratelow;
                }
                rate = rate/ChargeSquared/Charge*1.0e-7;
                /* must convert to cs and need to know the valid temp range */
                templow = 0.025*27.211396*TE1RYD/EVRYD*ChargeSquared;
                temphigh = 0.80*27.211396*TE1RYD/EVRYD*ChargeSquared;
                TeUse = MIN2((double)phycon.te,temphigh);
                temp = MAX2(TeUse,templow);
                Hydcs123_v = rate*gHi*sqrt(temp)/COLL_CONST;

                if( chType == 'p' )
                {
                        /* COLL_CONST is incorrect for protons, correct here */
                        Hydcs123_v *= pow( PROTON_MASS/ELECTRON_MASS, 1.5 );
                }
        }
        else if( ipHi == 4 || ipHi == 5 || ipHi == 6 )
        {
                /* n = 3
                 * for the rates involving n = 3, must do something different. */
                if( nelem < 1 )
                {
                        fprintf( ioQQQ, " insane charge given to Hydcs123\n" );
                        cdEXIT(EXIT_FAILURE);
                }
                else if( nelem == 1 )
                {
                        zlow = 2.;
                        Ratelow = He2cs123(ipLow,ipHi);
                        zhigh = 2.;
                        Ratehigh = Ratelow;
                }
                else if( nelem > 1 && nelem <= 5 )
                {
                        zlow = 2.;
                        Ratelow = He2cs123(ipLow,ipHi);
                        zhigh = 6.;
                        Ratehigh = C6cs123(ipLow,ipHi);
                }
                else if( nelem > 5 && nelem <= 9 )
                {
                        zlow = 6.;
                        Ratelow = C6cs123(ipLow,ipHi);
                        zhigh = 10.;
                        Ratehigh = Ne10cs123(ipLow,ipHi);
                }
                else if( nelem > 9 && nelem <= 19 )
                {
                        zlow = 10.;
                        Ratelow = Ne10cs123(ipLow,ipHi);
                        zhigh = 20.;
                        Ratehigh = Ca20cs123(ipLow,ipHi);
                }
                else if( nelem > 19 && nelem <= 25 )
                {
                        zlow = 20.;
                        Ratelow = Ca20cs123(ipLow,ipHi);
                        zhigh = 26.;
                        Ratehigh = Fe26cs123(ipLow,ipHi);
                }
                /*>>>chng 98 dec 17, to else to stop comment from good compilers*/
                /*else if( nelem > 26 )*/
                else
                {
                        Charge = 26.;
                        zlow = 26.;
                        Ratelow = Fe26cs123(ipLow,ipHi);
                        zhigh = 26.;
                        Ratehigh = Ratelow;
                }

                /* linearly interpolate */
                if( fp_equal( zlow, zhigh ) )
                {
                        rate = Ratelow;
                }
                else
                {
                        slope = (Ratehigh - Ratelow)/(zhigh - zlow);
                        rate = slope*(Charge - zlow) + Ratelow;
                }

                Hydcs123_v = rate;

                /* the routines C6cs123, Ne10cs123, etc... do not resolve L for n>2 */
                /* dividing by N should roughly recover the original l-resolved data */
                Hydcs123_v /= 3.;
        }
        else
        {
                /* this branch 1-2s, 1-2p */
                if( nelem == 1 )
                {
                        /* this brance for helium, then return */
                        Hydcs123_v = He2cs123(ipLow,ipHi);
                        return( Hydcs123_v );
                }

                /* electron temperature in eV */
                tev = phycon.te / EVDEGK;
                /* energy in eV for hydrogenic species and these quantum numbers */
                EE = ChargeSquared*EVRYD*(1./QuanNLo/QuanNLo - 1./QuanNUp/QuanNUp);
                /* EE/kT for this transion */
                q = EE/tev;
                TeUse = MIN2(q,10.);
                /* q is now EE/kT but between 1 and 10 */
                q = MAX2(1.,TeUse);
                expq = exp(q);

                /* i must be 0 or 1 */
                ASSERT( i==0 || i==1 );
                C = C0[i] + C1[i]/Charge + C2[i]/ChargeSquared;
                D = D0[i] + D1[i]/Charge + D2[i]/ChargeSquared;

                /* following code changed so that ee1 always returns e1,
                 * orifinal version only returned e1 for x < 1 */
                /* use disabled e1: */
                /*if( q < 1. )*/
                /*{*/
                        /*rate = (B[i-1] + D*q)*exp(-q) + (A[i-1] + C*q - D*q*q)**/
                          /*ee1(q);*/
                /*}*/
                /*else*/
                /*{*/
                        /*rate = (B[i-1] + D*q) + (A[i-1] + C*q - D*q*q)*ee1(q);*/
                /*}*/
                /*rate *= 8.010e-8/2./ChargeSquared/tev*sqrt(tev);*/
                /* convert to de-excitation */
                /*if( q < 1. )*/
                /*{*/
                        /*rate = rate*exp(q)*gLo/gHi;*/
                /*}*/
                /*else*/
                /*{*/
                        /*rate = rate*gLo/gHi;*/
                /*}*/

                /*>>>chng 98 dec 17, ee1 always returns e1 */
                rate = (B[i] + D*q)/expq + (A[i] + C*q - D*q*q)*
                          ee1(q);
                rate *= 8.010e-8/2./ChargeSquared/tev*sqrt(tev);
                /* convert to de-excitation */
                rate *= expq*gLo/gHi;

                /* convert to cs */
                Hydcs123_v = rate*gHi*phycon.sqrte/COLL_CONST;
        }
        return( Hydcs123_v );
}

/*C6cs123 line collision rates for lower levels of hydrogenic carbon, n=1,2,3 */
STATIC double C6cs123(long int i, 
  long int j)
{
        double C6cs123_v, 
          TeUse, 
          t, 
          x;
        static const double a[3] = {-92.23774,-1631.3878,-6326.4947};
        static const double b[3] = {-11.93818,-218.3341,-849.8927};
        static const double c[3] = {0.07762914,1.50127,5.847452};
        static const double d[3] = {78.401154,1404.8475,5457.9291};
        static const double e[3] = {332.9531,5887.4263,22815.211};

        DEBUG_ENTRY( "C6cs123()" );

        /* These are fits to Table 5 of
         * >>refer      c6      cs      Aggarwal, K.M., & Kingston, A.E. 1991, J Phys B, 24, 4583
         * C VI collision rates for 1s-3l, 2s-3l, and 2p-3l, 
         * principal quantum numbers n and l.
         *
         * i is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         * j is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d)
         * 1s-2s,2p is not done here.
         * check temperature: fits only good between 3.8 < log Te < 6.2
         */
        /* arrays for fits of 3 transitions see the code below for key: */

        TeUse = MAX2(phycon.te,6310.);
        t = MIN2(TeUse,1.6e6);
        x = log10(t);

        if( i == 1 && j == 2 )
        {
                /* 1s - 2s (first entry) */
                fprintf( ioQQQ, " Carbon VI 2s-1s not done in C6cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && j == 3 )
        {
                /* 1s - 2p (second entry) */
                fprintf( ioQQQ, " Carbon VI 2p-1s not done in C6cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 1s - 3 (first entry) */
                C6cs123_v = a[0] + b[0]*x + c[0]*pow2(x)*sqrt(x) + d[0]*log(x) + 
                  e[0]*log(x)/pow2(x);
        }
        else if( i == 2 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2s - 3 (second entry)         */
                C6cs123_v = a[1] + b[1]*x + c[1]*pow2(x)*sqrt(x) + d[1]*log(x) + 
                  e[1]*log(x)/pow2(x);
        }
        else if( i == 3 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2p - 3s (third entry) */
                C6cs123_v = a[2] + b[2]*x + c[2]*pow2(x)*sqrt(x) + d[2]*log(x) + 
                  e[2]*log(x)/pow2(x);
        }
        else
        {
                fprintf( ioQQQ, "  insane levels for C VI n=1,2,3 !!!\n" );
                cdEXIT(EXIT_FAILURE);
        }
        return( C6cs123_v );
}

/*Ca20cs123 line collision rates for lower levels of hydrogenic calcium, n=1,2,3 */
STATIC double Ca20cs123(long int i, 
  long int j)
{
        double Ca20cs123_v, 
          TeUse, 
          t, 
          x;
        static const double a[3] = {-12.5007,-187.2303,-880.18896};
        static const double b[3] = {-1.438749,-22.17467,-103.1259};
        static const double c[3] = {0.008219688,0.1318711,0.6043752};
        static const double d[3] = {10.116516,153.2650,717.4036};
        static const double e[3] = {45.905343,685.7049,3227.2836};

        DEBUG_ENTRY( "Ca20cs123()" );

        /* 
         * These are fits to Table 5 of
         * >>refer      ca20    cs      Aggarwal, K.M., & Kingston, A.E. 1992, J Phys B, 25, 751
         * Ca XX collision rates for 1s-3l, 2s-3l, and 2p-3l, 
         * principal quantum numbers n and l.
         *      
         * i is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         * j is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d)
         * 1s-2s,2p is not done here.
         * check temperature: fits only good between 5.0 < log Te < 7.2
         */

        /* arrays for fits of 3 transitions see the code below for key: */

        TeUse = MAX2(phycon.te,1.0e5);
        t = MIN2(TeUse,1.585e7);
        x = log10(t);

        if( i == 1 && j == 2 )
        {
                /* 1s - 2s (first entry) */
                fprintf( ioQQQ, " Ca XX 2s-1s not done in Ca20cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && j == 3 )
        {
                /* 1s - 2p (second entry) */
                fprintf( ioQQQ, " Ca XX 2p-1s not done in Ca20cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && ( j == 4 || j == 5 || j == 6 ))
        {
                /* 1s - 3 (first entry) */
                Ca20cs123_v = a[0] + b[0]*x + c[0]*pow2(x)*sqrt(x) + d[0]*log(x) + 
                  e[0]*log(x)/pow2(x);
        }
        else if( i == 2 && ( j == 4 || j == 5 || j == 6 ))
        {
                /* 2s - 3 (second entry)         */
                Ca20cs123_v = a[1] + b[1]*x + c[1]*pow2(x)*sqrt(x) + d[1]*log(x) + 
                  e[1]*log(x)/pow2(x);
        }
        else if( i == 3 && ( j == 4 || j == 5 || j == 6 ))
        {
                /* 2p - 3s (third entry) */
                Ca20cs123_v = a[2] + b[2]*x + c[2]*pow2(x)*sqrt(x) + d[2]*log(x) + 
                  e[2]*log(x)/pow2(x);
        }
        else
        {
                fprintf( ioQQQ, "  insane levels for Ca XX n=1,2,3 !!!\n" );
                cdEXIT(EXIT_FAILURE);
        }
        return( Ca20cs123_v );
}

/*Ne10cs123 line collision rates for lower levels of hydrogenic neon, n=1,2,3 */
STATIC double Ne10cs123(long int i, 
  long int j)
{
        double Ne10cs123_v, 
          TeUse, 
          t, 
          x;
        static const double a[3] = {3.346644,151.2435,71.7095};
        static const double b[3] = {0.5176036,20.05133,13.1543};
        static const double c[3] = {-0.00408072,-0.1311591,-0.1099238};
        static const double d[3] = {-3.064742,-129.8303,-71.0617};
        static const double e[3] = {-11.87587,-541.8599,-241.2520};

        DEBUG_ENTRY( "Ne10cs123()" );

        /*  These are fits to Table 5 of
         *  >>refer     ne10    cs      Aggarwal, K.M., & Kingston, A.E. 1991, PhyS, 44, 517
         *  Ne X collision rates for 1s-3, 2s-3l, and 2p-3l, 
         *  principal quantum numbers n and l.
         *
         *  i is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         *  j is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d)
         *  1s-2s,2p is not done here.
         *  check temperature: fits only good between 3.8 < log Te < 6.2
         * */
        /* arrays for fits of 3 transitions see the code below for key: */

        TeUse = MAX2(phycon.te,6310.);
        t = MIN2(TeUse,1.6e6);
        x = log10(t);

        if( i == 1 && j == 2 )
        {
                /* 1s - 2s (first entry) */
                fprintf( ioQQQ, " Neon X 2s-1s not done in Ne10cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && j == 3 )
        {
                /* 1s - 2p (second entry) */
                fprintf( ioQQQ, " Neon X 2p-1s not done in Ne10cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 1s - 3 (first entry) */
                Ne10cs123_v = a[0] + b[0]*x + c[0]*pow2(x)*sqrt(x) + d[0]*log(x) + 
                  e[0]*log(x)/pow2(x);
        }
        else if( i == 2 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2s - 3 (second entry)         */
                Ne10cs123_v = a[1] + b[1]*x + c[1]*pow2(x)*sqrt(x) + d[1]*log(x) + 
                  e[1]*log(x)/pow2(x);
        }
        else if( i == 3 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2p - 3s (third entry) */
                Ne10cs123_v = a[2] + b[2]*x + c[2]*pow2(x)*sqrt(x) + d[2]*log(x) + 
                  e[2]*log(x)/pow2(x);
        }
        else
        {
                fprintf( ioQQQ, "  insane levels for Ne X n=1,2,3 !!!\n" );
                cdEXIT(EXIT_FAILURE);
        }
        return( Ne10cs123_v );
}

/*He2cs123 line collision strengths for lower levels of helium ion, n=1,2,3, by K Korista */
STATIC double He2cs123(long int i, 
  long int j)
{
        double He2cs123_v, 
          t;
        static const double a[11]={0.12176209,0.32916723,0.46546497,0.044501688,
          0.040523277,0.5234889,1.4903214,1.4215094,1.0295881,4.769306,9.7226127};
        static const double b[11]={0.039936166,2.9711166e-05,-0.020835863,3.0508137e-04,
          -2.004485e-15,4.41475e-06,1.0622666e-05,2.0538877e-06,0.80638448,2.0967075e-06,
          7.6089851e-05};
        static const double c[11]={143284.77,0.73158545,-2.159172,0.43254802,2.1338557,
          8.9899702e-06,-2.9001451e-12,1.762076e-05,52741.735,-2153.1219,-3.3996921e-11};

        DEBUG_ENTRY( "He2cs123()" );

        /* These are fits to Table 2
         * >>refer      he2     cs      Aggarwal, K.M., Callaway, J., Kingston, A.E., Unnikrishnan, K.
         * >>refercon   1992, ApJS, 80, 473
         * He II collision rates for 1s-2s, 1s-2p, 1s-3s, 1s-3p, 1s-3d, 2s-3s, 2s-3p, 2s-3d,
         * 2p-3s, 2p-3p, and 2p-3d. 
         * principal quantum numbers n and l.
         *
         * i is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         * j is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d)
         * check temperature: fits only good between 5,000K and 500,000K
         * */
        /* array for fits of 11 transitions see the code below for key: */

        t = phycon.te;
        if( t < 5000. )
        {
                t = 5000.;
        }
        else if( t > 5.0e05 )
        {
                t = 5.0e05;
        }

        /**************fits begin here**************
         * */
        if( i == 1 && j == 2 )
        {
                /* 1s - 2s (first entry) */
                He2cs123_v = a[0] + b[0]*exp(-t/c[0]);
        }
        else if( i == 1 && j == 3 )
        {
                /* 1s - 2p (second entry) */
                He2cs123_v = a[1] + b[1]*pow(t,c[1]);
        }
        else if( i == 1 && j == 4 )
        {
                /* 1s - 3s (third entry) */
                He2cs123_v = a[2] + b[2]*log(t) + c[2]/log(t);
        }
        else if( i == 1 && j == 5 )
        {
                /* 1s - 3p (fourth entry) */
                He2cs123_v = a[3] + b[3]*pow(t,c[3]);
        }
        else if( i == 1 && j == 6 )
        {
                /* 1s - 3d (fifth entry) */
                He2cs123_v = a[4] + b[4]*pow(t,c[4]);
        }
        else if( i == 2 && j == 4 )
        {
                /* 2s - 3s (sixth entry)         */
                He2cs123_v = (a[5] + c[5]*t)/(1 + b[5]*t);
        }
        else if( i == 2 && j == 5 )
        {
                /* 2s - 3p (seventh entry) */
                He2cs123_v = a[6] + b[6]*t + c[6]*t*t;
        }
        else if( i == 2 && j == 6 )
        {
                /* 2s - 3d (eighth entry) */
                He2cs123_v = (a[7] + c[7]*t)/(1 + b[7]*t);
        }
        else if( i == 3 && j == 4 )
        {
                /* 2p - 3s (ninth entry) */
                He2cs123_v = a[8] + b[8]*exp(-t/c[8]);
        }
        else if( i == 3 && j == 5 )
        {
                /* 2p - 3p (tenth entry) */
                He2cs123_v = a[9] + b[9]*t + c[9]/t;
        }
        else if( i == 3 && j == 6 )
        {
                /* 2p - 3d (eleventh entry) */
                He2cs123_v = a[10] + b[10]*t + c[10]*t*t;
        }
        else
        {
                /**************fits end here************** */
                fprintf( ioQQQ, "  insane levels for He II n=1,2,3 !!!\n" );
                cdEXIT(EXIT_FAILURE);
        }
        return( He2cs123_v );
}

/*Fe26cs123 line collision rates for lower levels of hydrogenic iron, n=1,2,3 */
STATIC double Fe26cs123(long int i, 
  long int j)
{
        double Fe26cs123_v, 
          TeUse, 
          t, 
          x;
        static const double a[3] = {-4.238398,-238.2599,-1211.5237};
        static const double b[3] = {-0.4448177,-27.06869,-136.7659};
        static const double c[3] = {0.0022861,0.153273,0.7677703};
        static const double d[3] = {3.303775,191.7165,972.3731};
        static const double e[3] = {15.82689,878.1333,4468.696};

        DEBUG_ENTRY( "Fe26cs123()" );

        /*  These are fits to Table 5 of
         *  >>refer     fe26    cs      Aggarwal, K.M., & Kingston, A.E. 1993, ApJS, 85, 187
         *  Fe XXVI collision rates for 1s-3, 2s-3, and 2p-3, 
         *  principal quantum numbers n and l.
         *
         *  i is the lower level and runs from 1 to 3 (1s, 2s, 2p)
         *  j is the upper level and runs from 2 to 6 (2s, 2p, 3s, 3p, 3d)
         *  1s-2s,2p is not done here.
         *  check temperature: fits only good between 5.2 < log Te < 7.2
         *  */
        /*  arrays for fits of 3 transitions see the code below for key: */

        TeUse = MAX2(phycon.te,1.585e5);
        t = MIN2(TeUse,1.585e7);
        x = log10(t);

        if( i == 1 && j == 2 )
        {
                /* 1s - 2s (first entry) */
                fprintf( ioQQQ, " Fe XXVI 2s-1s not done in Fe26cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && j == 3 )
        {
                /* 1s - 2p (second entry) */
                fprintf( ioQQQ, " Fe XXVI 2p-1s not done in Fe26cs123\n" );
                cdEXIT(EXIT_FAILURE);
        }

        else if( i == 1 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 1s - 3 (first entry) */
                Fe26cs123_v = a[0] + b[0]*x + c[0]*pow2(x)*sqrt(x) + d[0]*log(x) + 
                  e[0]*log(x)/pow2(x);
        }
        else if( i == 2 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2s - 3 (second entry)         */
                Fe26cs123_v = a[1] + b[1]*x + c[1]*pow2(x)*sqrt(x) + d[1]*log(x) + 
                  e[1]*log(x)/pow2(x);
        }
        else if( i == 3 && ( j == 4 || j == 5 || j == 6 ) )
        {
                /* 2p - 3s (third entry) */
                Fe26cs123_v = a[2] + b[2]*x + c[2]*pow2(x)*sqrt(x) + d[2]*log(x) + 
                  e[2]*log(x)/pow2(x);
        }
        else
        {
                fprintf( ioQQQ, "  insane levels for Ca XX n=1,2,3 !!!\n" );
                cdEXIT(EXIT_FAILURE);
        }
        return( Fe26cs123_v );
}


STATIC double CS_ThermAve_PR78(long ipISO, long nelem, long nHi, long nLo, double deltaE, double temp )
{

        double coll_str;

        DEBUG_ENTRY( "CS_ThermAve_PR78()" );

        global_ipISO = ipISO;
        global_nelem = nelem;
        global_nHi = nHi;
        global_nLo = nLo;
        global_deltaE = deltaE;

        kTRyd = temp / TE1RYD;

        if( !iso_ctrl.lgCS_therm_ave[ipISO] )
        {
                /* Must do some thermal averaging for densities greater
                 * than about 10000 and less than about 1e10,
                 * because kT gives significantly different results.
                 * Still, do sparser integration than is done below */
                if( (dense.eden > 10000.) && (dense.eden < 1E10 ) )
                {
                        coll_str =  qg32( 0.0, 6.0, Therm_ave_coll_str_int_PR78);
                }
                else
                {
                        /* Do NOT average over Maxwellian */
                        coll_str = CS_PercivalRichards78( kTRyd );
                }
        }
        else
        {
                /* DO average over Maxwellian */
                coll_str =  qg32( 0.0, 1.0, Therm_ave_coll_str_int_PR78);
                coll_str += qg32( 1.0, 10.0, Therm_ave_coll_str_int_PR78);
        }

        return coll_str;
}

/* The integrand for calculating the thermal average of collision strengths */
STATIC double Therm_ave_coll_str_int_PR78( double EOverKT )
{
        double integrand;

        DEBUG_ENTRY( "Therm_ave_coll_str_int_PR78()" );

        integrand = exp( -1.*EOverKT ) * CS_PercivalRichards78( EOverKT * kTRyd );

        return integrand;
}

STATIC double CS_PercivalRichards78( double Ebar )
{
        double cross_section, coll_str;
        double stat_weight;
        double A, D, L, F, G, H;
        double np, n, s, Z_3, xPlus, xMinus, y;
        long ipISO, nelem;

        DEBUG_ENTRY( "CS_PercivalRichards78()" );

        if( Ebar < global_deltaE )
        {
                DEBUG_ENTRY( "CS_PercivalRichards78()" );
                return 0.;
        }

        ipISO = global_ipISO;
        nelem = global_nelem;
        np = (double)global_nHi;
        n  = (double)global_nLo;
        s = np - n;
        ASSERT( s > 0. );

        A = (8./3./s) * pow(np/s/n, 3.) * (0.184 - 0.04 * pow( s, -0.66)) * pow( 1. - 0.2*s/n/np, 1.+2.*s);

        Z_3 = (double)(nelem + 1. - ipISO);

        D = exp( - Z_3 * Z_3 / n / np / Ebar / Ebar );

        L = log( (1. + 0.53 * Ebar * Ebar * n * np / Z_3 / Z_3) / (1. + 0.4*Ebar) );

        F = pow( 1. - 0.3 * s * D / n /np, 1. + 2.*s );

        G = 0.5* POW3( Ebar * n * n / Z_3 / np );

        xPlus  = 2. * Z_3 / ( n * n * Ebar * ( sqrt( 2. - n*n/np/np ) + 1. ) );
        xMinus = 2. * Z_3 / ( n * n * Ebar * ( sqrt( 2. - n*n/np/np ) - 1. ) );

        y = 1. / (1. - D * log ( 18. * s )/ 4. / s);

        H  = POW2( xMinus) * log( 1. + 2.*xMinus/3. ) / ( 2.*y + 1.5*xMinus );
        H -= POW2( xPlus ) * log( 1. + 2.* xPlus/3. ) / ( 2.*y + 1.5*xPlus );

        /* this is the LHS of equation 1 of PR78 */
        cross_section  = (A*D*L + F*G*H);
        /* this is the result after solving equation 1 for the cross section */
        cross_section *= PI * POW2( n * n * BOHR_RADIUS_CM / Z_3 ) / Ebar;

        if( ipISO == ipH_LIKE )
                stat_weight = 2. * n * n;
        else if( ipISO == ipHE_LIKE )
                stat_weight = 4. * n * n;
        else
                TotalInsanity();

        /* convert to collision strength */
        coll_str = cross_section * stat_weight * Ebar / ( PI * POW2( BOHR_RADIUS_CM ) );
        return coll_str;
}

#if     0
STATIC void TestPercivalRichards( void )
{
        double CStemp;

        /* this reproduces Table 1 of PR78 */
        for( long i=0; i<5; i++ )
        {       
                double Ebar[5] = {0.1, 0.4, 0.8, 1.0, 10.};
                
                CStemp = CS_PercivalRichards78( 0, 2, 12, 10, Ebar[i] );
        }

        /* this reproduces Table 2 of PR78 */
        for( long i=0; i<5; i++ )
        {       
                double Ebar[5] = {0.1, 0.4, 0.8, 1.0, 10.};
                
                CStemp = CS_ThermAve_PR78( ipISO, 0, N_(ipHi), N_(ipLo), phycon.te );
        }
        
        return;
}
#endif

realnum HydroCSInterp(long int nelem,
                                 long int ipHi,
                                 long int ipLo,
                                 long int ipCollider )
{
        double CStemp;
        long ipISO = ipH_LIKE;

        DEBUG_ENTRY( "HydroCSInterp()" );

        if( !iso_ctrl.lgColl_excite[ipISO] )
                return 0.;

        /* This set of collision strengths should only be used
         * if the Storey and Hummer flag is set */
        if( opac.lgCaseB_HummerStorey )
        {
                if( N_(ipLo) == N_(ipHi) )
                {
                        if( N_(ipHi) <= iso_sp[ipH_LIKE][nelem].n_HighestResolved_max &&
                                abs( L_(ipLo) - L_(ipHi) ) != 1 )
                        {
                                /* if delta L is not +/- 1, set collision strength to zero. */
                                CStemp = 0.;
                        }
                        else
                        {
                                CStemp =  CS_l_mixing_PS64( 
                                        nelem,
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].lifetime(),
                                        nelem+1.-ipH_LIKE,
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].n(),
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].l(),
                                        iso_sp[ipH_LIKE][nelem].st[ipHi].g(),
                                        ipCollider);
                        }
                }

                else 
                {
                        if( N_(ipHi) <= iso_sp[ipH_LIKE][nelem].n_HighestResolved_max &&
                                abs( L_(ipLo) - L_(ipHi) ) != 1 )
                        {
                                /* if delta L is not +/- 1, set collision strength to zero. */
                                CStemp = 0.;
                        }
                        else if( ipCollider == ipELECTRON )
                        {
                                CStemp = CS_ThermAve_PR78( ipH_LIKE, nelem, N_(ipHi), N_(ipLo), 
                                        iso_sp[ipH_LIKE][nelem].trans(ipHi,ipLo).EnergyErg() / EN1RYD ,  phycon.te );
                        }
                        else
                                CStemp = 0.;
                }
        }
        else
        {
                /* HCSAR_interp interpolates on a table to return R-matrix collision strengths
                 * for hydrogen only */
                if( nelem==ipHYDROGEN && ipCollider==ipELECTRON && N_(ipHi) <= 5 && ( N_(ipHi) != N_(ipLo) ) )
                {
                        CStemp = HCSAR_interp(ipLo,ipHi);
                }
                else if( nelem==ipHYDROGEN && ipCollider==ipELECTRON && ( N_(ipHi) != N_(ipLo) ) )
                {
                        CStemp = hydro_vs_deexcit( ipH_LIKE, nelem, ipHi, ipLo, iso_sp[ipH_LIKE][nelem].trans(ipHi,ipLo).Emis().Aul() );
                }
                else if( nelem>ipHYDROGEN && ipCollider==ipELECTRON && N_(ipHi) <= 3 && N_(ipLo) < 3 )
                {
                        CStemp = Hydcs123(ipLo + 1,ipHi + 1,nelem,'e');
                }
                else if( nelem>ipHYDROGEN && ipCollider==ipPROTON && ipHi==ipH2p && ipLo==ipH2s )
                {
                        CStemp = Hydcs123(ipLo + 1,ipHi + 1,nelem,'p');
                }
                else if( N_(ipLo) == N_(ipHi) )
                {
                        if( iso_ctrl.lgCS_Vrinceanu[ipH_LIKE] )
                        {
                                CStemp = CS_l_mixing_VF01(ipH_LIKE, nelem,
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].n(),
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].l(),
                                        iso_sp[ipH_LIKE][nelem].st[ipHi].l(),
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].S(),
                                        phycon.te, 
                                        ipCollider );
                        }
                        else
                                CStemp = CS_l_mixing_PS64( 
                                        nelem,
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].lifetime(),
                                        nelem+1.-ipH_LIKE,
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].n(),
                                        iso_sp[ipH_LIKE][nelem].st[ipLo].l(),
                                        iso_sp[ipH_LIKE][nelem].st[ipHi].g(),
                                        ipCollider);
                }
                else
                {
                        ASSERT( N_(ipHi) != N_(ipLo) );
                        /* highly excited levels */
                        CStemp = CS_VS80( ipH_LIKE, nelem, ipHi, ipLo, 
                                iso_sp[ipH_LIKE][nelem].trans(ipHi,ipLo).Emis().Aul(),
                                phycon.te,
                                ipCollider );
                }
        }

        return (realnum)CStemp;
}

---