;+
; NAME:
;  rt_szss96_gammaf4
; PURPOSE: (one line)
;  escape function for CH4 7.6 micron cooling
; DESCRIPTION:
;  escape function for CH4 7.6 micron cooling
; CATEGORY:
;  RT
; CALLING SEQUENCE:
;  kcoef = rt_szss96_coefv4(t)
; INPUTS:
;  t - temperature (K) [nz array]
; OPTIONAL INPUT PARAMETERS:
; KEYWORD INPUT PARAMETERS:
;  codetype
;    'FORTRAN' - call routines from plutot.f
;    'FORTEST' - native IDL routines that reproduce the fortran
;    'IDL' - idl code, without the restriction of needing to reproduce fortran
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  kcoeff   number column density [nz,ng] (cm^2)
; COMMON BLOCKS:
; SIDE EFFECTS:
; RESTRICTIONS:
;  Modifies atm
; PROCEDURE:
;  Gamma_f4, eqn (30) of Strobel, Zhu, Summers and Stevens 1996 
; EXAMPLE:
;
;  atm = rt_szss96_atmread('',0,code='FORTRAN')
; kcoef = rt_szss96_kcoefv4(atm.t, 2L)
; rho1 = (atm.n[*,1]/atm.ncol) * (16.0D0/28.0D0)
; gamma_f4 = rt_szss96_gammaf4(atm.p, rho1, kcoef, gamma_f4inf)
; 
; MODIFICATION HISTORY:
;  Written 2007 Aug 31, Leslie Young SwRI
;  based on plutot.f, written by Zun Zhu
;-

function rt_szss96_gammaf4, p, rho1, kcoef, gamma_f4inf

    fcn = 'rt_szss96_gammav4'
    
    if not keyword_set(codetype) then codetype = 'FORTRAN'

    case codetype of
        'FORTRAN': begin
            get_ch4all,GG,WW,TREF
            if tref[0] ne 40.d then begin
                input6
            endif

            PRE = p / 10.d

            KM = n_elements(PRE)
            xkz_cgs = kcoef / (16. * 1.3804D-16/8314d4)
            XKZ = xkz_cgs / 10.d

            gamm12mat,PRE,RHO1,KM,XKZ,GAM1,GAMN4
            gamma_f4 = gam1
            gamma_f4inf = gamn4
            return, gamma_f4

        end
        else: begin
            print, fcn, ': code type ', codetype, ' not implemented'
            return, -1
        end
    endcase

end