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         Version 2.03
 
         ESK parameterization of nuclear shadowing of parton distributions
         is replaced by a user implemented subroutine SHADOW. Users can replace
         this subroutine with their own parametrization
 
         Versio 2.02
 
         in order to fit the total cross section and dn/dy in pp or ppbar
         collisions the pt cut-off now varies with energy roughly as
         p0=1.3+0.09*log(sqrt(s)/10)+0.065*log(sqrt(s)/10)**2
 
 
         Version 2.01
 
         Major modification started on Feb. 22, 1999:
         Include options for different parametrization of parton distributions.
         IHPR2(7):(D=4)
                =1 or 2 Duke-Owns set 1 or 2
                =3 MRS D-' parametrization
                =4 GRV HO
                =5 CTEQ 2pM
 
 
         IHPR2(6):(D=1)
                =1 the original HIJING parametrization of shadowing
                =2 Eskola-Kolhinen-Salgado parametrization
 
         *****************
         *               *
         * Version 2.00  *
         *               *
         *****************
 
         Modification Oct. 8, 1998. In hijing, log(ran(nseed)) occasionally
         causes overfloat. It is modified to log(max(ran(nseed),1.0e-20)).
 
         replaces all the generic random number generator ran(nseed) by the 
         portable random number generator in jetset  RLU(0).
  
         add the following common block to store the formation time and position
         of each hadron
         COMMON/HIMAIN3/VATT(130000,4)
         For directly produced or massless particles (gamma, dilepton, etc),
         we set VATT(I,4)=-10, and VATT(I,1-3)=0
         HIPR1(50)=particle formation time in rest-frame with default value 
         1.0 fm
 
 
 
         Version 1.36
 
 
         (5/30/98) Some statements in HIJSFT ae modified to avoid questionable
         branch into another IF block (new compiler on alpha machines does not
         like this).
 
         Nothing important has been changed here. A few 'garbage' has been
         cleaned up here, like common block HIJJET3 for the sea quark strings
         which were originally created to implement the DPM scheme which
         later was abadoned in the final version. The lines which operate
         on these data are also deleted in the program.
 
 
 
         *************************
         *                       *
         *     Version 1.35      *
         *                       *
         *************************
 
         Last modification on Feb. 24, 1997.
         There are some changes in the program: subroutine HARDJET is now
         consolidated with HIJHRD. HARDJET is used to re-initiate PYTHIA
         for the triggered hard processes. Now that is done  altogether
         with other normal hard processes in modified JETINI. In the new
         version one calls JETINI every time one calls HIJHRD. In the new
         version the effect of the isospin of the nucleon on hard processes,
         especially direct photons is correctly considered.
         For A+A collisions, one has to initilize pythia
         separately for each type of collisions, pp, pn,np and nn,
         or hp and hn for hA collisions. In JETINI we use the following
         catalogue for different types of collisions:
         h+h: h+h (I_TYPE=1)
         h+A: h+p (I_TYPE=1), h+n (I_TYPE=2)
         A+h: p+h (I_TYPE=1), n+h (I_TYPE=2)
         A+A: p+p (I_TYPE=1), p+n (I_TYPE=2), n+p (I_TYPE=3), n+n (I_TYPE=4)
 
 
         ****************************
         *                          *
         *       Version 1.34       *
         *                          *
         ****************************
 
        Last modification on January 5, 1998. Two misstakes are corrected in
        function G. A Misstake in the subroutine Parton is also corrected.
        (These are pointed out by Yasushi Nara).
 
 
        Last modifcation on April 10, 1996. To conduct final
        state radiation, PYTHIA reorganize the two scattered
        partons and their final momenta will be a little
        different. The summed total momenta of the partons
        from the final state radiation are stored in HINT1(26-29)
        and HINT1(36-39) which are little different from 
        HINT1(21-24) and HINT1(41-44).
 
 
 
 
 
         *************************
         *                       *
         *      Version 1.33     *
         *                       *
         *************************
 
        Last modfication  on September 11, 1995. When HIJING and
        PYTHIA are initialized, the shadowing is evaluated at
        b=0 which is the maximum. This will cause overestimate
        of shadowing for peripheral interactions. To correct this
        problem, shadowing is set to zero when initializing. Then
        use these maximum  cross section without shadowing as a
        normalization of the Monte Carlo. This however increase
        the computing time. IHNT2(16) is used to indicate whether
        the sturcture function is called for (IHNT2(16)=1) initialization
        or for (IHNT2(16)=0)normal collisions simulation
 
        Last modification on Aagust 28, 1994. Two bugs associate
        with the impact parameter dependence of the shadowing is
        corrected.
 
         *********************************
         *       HIJING version 1.31     *
         *********************************
 
         No major change has been made in this version. A bug 
 associated with triggering direct photon is corrected. This 
 problem was reported by Jim Carroll and Mike Beddo. Another 
 bug in tracing decay trees reported by Matt Bloomer was also 
 corrected.
 
         Another feature of triggered jet production (including 
 direct photon) in HIJING needs to be clarified here. The energy 
 and momentum stored in HINT1(21)-HINT1(25); HINT1(31)-HINT1(35); 
 HINT1(41)-HINT1(45); and HINT1(51)-HINT1(55) are the momenta 
 of the hard scattered partons in the lowest order calculation. 
 To include the higher order correction, final state radiations 
 are implemented. In this implementation, momentum and energy 
 are reshuffled so that the momentum and energy you find in the 
 finally produced parton or particle might not match those in 
 HINT1(21)-HINT1(55). But the momentum is still balanced for 
 the back-to-back jets (or jet and photon). So information in 
 HINT1(21)-HINT1(55) still give the right direction of the two 
 high pt jets.
 
         *********************************
         *       HIJING Version 1.30     *
         *********************************
 
         The option to trig on heavy quark production (charm IHPR2(18)=0 
 or beauty IHPR2(18)=1) is added. To do this, set IHPR2(3)=3. For inclusive 
 production, one should reset HIPR1(10)=0.0. One can also trig larger pt
 QQbar production by giving HIPR1(10) a nonvanishing value. The mass 
 of the heavy quark in the calculation of the cross section (HINT1(59)-
 -HINT1(65)) is given by HIPR1(7) (the default is the charm mass D=1.5). 
 We also include a separate K-factor for heavy quark and direct photon 
 production by HIPR1(23)(D=2.0).
 
         *********************************
         *       HIJING version 1.20     *
         *********************************
 
 Beside some modifications to correct some minor errors, there three
 major changes since the first version.
 
         (1) An option is added to keep the information of all 
 particles including the decay chains. The switch of this option 
 is IHPR(21)=1 (default=0). The array KATT(130000,2) in 
 COMMON/HIMAIN2/ is expanded to KATT(130000,4). K(I,3) is the line 
 number of the parent particle of the current line which is produced 
 via a decay. KATT(I,4) is the status number of the particle: 11=particle
 which has decayed; 1=finally or directly produced particle.
 
         (2)Heavy flavor production processes through q+\bar{q}-->c+\bar{c}
 and g+g-->c+\bar{c} have been switched on. Charm production is the default, 
 B-quark option is IHPR2(18)=1 (default=0). Note that when B-quark production
 is switched on, charm quark is automatically off.
 
         (3) A subroutine  PROFILE(XB) is added to assist the simulation 
 of minimum biased events of proton-nucleus and nucleus-nucleus collisions. 
 Refer to the examples in hijing.tex for the simulation.
 
 
 

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