externals_2017.f
  -Program to calculate measured cross sections
  -Input files
    --input/cross-sec-data/*: cross section data for fits & interpolations
    --input/d2model/parms.dat: parameters for d2model
    --input/externals/externals.inp: list of i/o files which are fed into externals_2017.f 
    --input/grids/*.inp: Input kinematics file listing variables: E0, Ep, theta, W2, Q2
    --input/targets/*.targ: Contains target & input parameters for the externals code
   
  -Output files:
    --output/externals/externals.out: Output file from externals code with radiative corrections
    --output/externals/*.out: Output file from externals code with diagnostics information

externals.inp
  -List of i/o files which are fed into externals_2017.f 
  -The first line is a comment
  -Dependent files:
    --eg1b.inp (second line)
      ---EXTERNAL_RUNPLAN (UNIT=7)
      ---Input kinematics file listing variables: E0, Ep, theta, W2, Q2 -> make_grid.C prints these
      ---Code assumes that first six lines of file are comments. This reading is done in 
         subroutine READIN_EXT
      ---Only E0, Ep, and theta are read in by the externals code, W2 and Q2 
         are supplemental information for the user
    --eg1b.targ (third line)
      ---EXTERNAL_TARGET (UNIT=5)
      ---Contains input parameters for the externals code
      ---Has a very specific format read (see subroutine READIN_EXT) so must be careful about format
      ---First 3 line read into COMMENT array then skips a line
      ---5th and 6th lines read in IA and IZ with format 15x,i5 then skips a line
        ----IA and IZ are the atomic number and charge of target.
      ---8th and 9th lines read in AVGA and AVGM with format 15x,f14.8 then skips a line
        ----If AVGA and AVGM are zero then calculated in subroutine weiz. For A>4 uses
	    the Weisacker mass formula. 
      ---11th line reads in TARGET with format 20x,A7 then skips a line
        ----TARGET is used for specific experiments hardwired in the code to set the target
       	    radiation lengths in subroutine RADIATORS. If set to "readin" ( or any name
	    that is not hadrcoded in subroutine RADIATORS) , the radiation
	    lengths are set from input ttarg,twall,tbeam,tspec
	    Also the variable SMRDEP is set differently from default for certain experiments.
      ---13th-16th line reads in ttarg,twall,tbeam,tspec with format 15x,f14.8
      ---17th lines reads NSEG with format 15x,i5 then skips 2 lines
        ----NSEG sets number of segments for the SIMPSON rule integration. Nseg must be EVEN.
      ---20th line reads IG  with format 15x,i5 then  skips a line
        ----IG selects the elastic proton form factor model 
	    in subroutine NFORM ( see NFORM for list)
	    IG=15 use Bosted fit. Should be updated with more recent parametrizations.
      ---22nd line reads IDUT with format 15x,i5
        ----IDUT selects the elastic deuteron form factor model in subroutine NUC_FORM_FACTOR
      ---23nd line reads INEL_MODEL with format 15x,i5
        ----INEL_MODEL selects inelastic cross section model in INELAST.
	    INEL_MODEL = 4 selects F1F209 . Best option. Many older models available. 
      ---24th line reads PAULI_MODEL  with format 15x,i5
        ----PAULI_MODEL sets model in subroutine PAULI_SUPPRESSION.
            0 = old stein model; 1 = tsai model; 2 no suppression
            F1F2QE09 uses Pauli suppression model from Tsai RMP 46,816(74) eq.B54
      ---25th line reads NUC_METHOD  with format 15x,i5
        ----UC_METHOD 0=No cos(theta_k) integration; 1= cos(th_k) integration
      ---26th line reads NUC_MODEL with format 15x,i5
	----NUC_MODEL not used if INEL_MODEL=4.
    --output/externals/*.out (fourth line)
      ---EXTERNAL_OUT (UNIT=10)
      ---Output file from externals code with diagnostics information. 
      ---Has the table of kinematics and radiatied cross sections.
      ---Contains the following variables: beam energy, scattered electron energy, 
         scattered electron angle, x, q2, SIGMA_BORN+SIGMA_CORR, 
   	 sigma_qela(2) + sigma_elpk(2) + sigma_inel(2), sigma_elpk(2), sigma_qela(2), sigma_inel(2),
	 SIGMA_BORN, iesv, iqsv, iwsv, sigma_qela(1) + sigma_elpk(1) + sigma_inel(1), sigma_elastic
      ---Note: the variables iesv, iqsv, iwsv are filled when doeg1b flag is set to true 

make_grid.C
  -Defines the grid for rad-corr, writes an input file (*.inp) containing the 
  variables: E0, E, theta, W2, Q2 based on energy steps in scattered beam energy and angle
  -The produced input file is read by the externals_2017.f script

make_rc_dat.C
  -Converts the output from extern.out in to the *.dat format that is required for the
  Monte-Carlo re-weighting code

Flow: ./run_externals.sh -> ./make_grid -> ./externals_2017 -> ./make_rc_dat