--- /dev/null
+*
+* $Id$
+*
+* $Log$
+* Revision 1.1.1.2 1996/10/30 08:27:48 cernlib
+* Version 7.04
+*
+* Revision 1.1.1.1 1996/04/12 15:29:10 plothow
+* Version 7.01
+*
+*
+#include "pdf/pilot.h"
+C Version 2 CTEQ distribution function in a parametrized form.
+
+C By: J. Botts, H.L. Lai, J.G. Morfin, J.F. Owens, J. Qiu, W.K. Tung
+C & H. Weerts
+
+C To avoid the proliferation of parton distribution functions, we recommend
+C that these distributions should replace Version 1 CTEQ distributions for
+C general usage. The differences between the two sets of distributions, as
+C briefly described below, do not significantly affect most applications for
+C fixed-target and hadron-collider applications.
+
+C Both CTEQ1 and CTEQ2 distributions fit existing DIS, Drell-Yan and Direct
+C phton data with excellent chi-squares. They represent two distinct ways to
+C resolve the inconsistency between CCFR and NMC measurements on F2 at small-x
+C and the neutrino dimuon measurements of s(x), as discovered by the CTEQ1
+C analysis: in the CTEQ1 analysis, the F2 measurements of CCFR and NMC are
+C taken seriously, leaving out the dimuon information on s(x); whereas in the
+C CTEQ2 analysis, thelatest CCFR NLO dimuon analysis of s(x) is used (within
+C errors) as input butleaving out the small-x F2 data which conflict with this
+C input. The small-xbehavior of the parton distributions are contrained in the
+C latter case by thenewly released HERA data. For details, see our
+C forthcoming paper.
+
+C This file contains three versions of the same CTEQ2 parton distributions:
+C
+C Two "front-end" subprograms:
+C FUNCTION Ctq2pPf (Iset, Iparton, X, Q, Irt)
+C returns the PROBABILITY density for a GIVEN flavor;
+C SUBROUTINE Ctq2pPs(Iset, Pdf, XX, QQ, Irt)
+C returns an array of MOMENTUM densities for ALL flavors;
+C One lower-level subprogram:
+C FUNCTION Ctq2pPd (Iset, Iprtn, XX, QQ, Irt)
+C returns the MOMENTUM density of a GIVEN valence or sea distribution.
+C Supplementary functions to return the relevant QCD parameters and other
+C information concerning these distributions are also included (see below).
+
+C Since this is an initial distribution of version 2, it is
+C useful for the authors to maintain a record of the distribution list in
+C case there are revisions or corrections.
+C In the interest of maintaining the integrity of this package,
+C please do not freely distribute this program package; instead, refer any
+C interested colleagues to direct their request for a copy to:
+C Botts@hades.ifh.de or Lai@cteq11.pa.msu.edu
+
+C If you have detailed questions concerning these CTEQ2 distributions, direct
+C inquires to Botts, Lai (see above) or Wu-Ki Tung (Tung@msupa.pa.msu.edu).
+
+C -------------------------------------------
+C Detailed instructions follow.
+
+C Name convention for CTEQ distributions: CTEQnSx where
+C n : version number (currently n = 2)
+C S : factorization scheme label: = [M D L] for [MS-bar DIS LO]
+C resp.
+C x : special characteristics, if any
+C (e.g. S(F) for singular (flat) small-x, L for "LEP lambda value")
+
+C Explanation of functional arguments:
+
+C Iset is the set label; in this version, Iset = 1, 2, 3, 4, 5, 6
+C correspond to the following CTEQ global fits:
+
+C cteq2M : best fit in the MS-bar scheme
+C cteq2MS : singular small-x
+C cteq2MF : flat small-x
+C cteq2ML : large lambda (Lambda(5) = 220 MeV)
+
+C cteq2L : best fit in Leading order QCD
+
+C cteq2D : best fit in the DIS scheme
+
+C Iprtn is the parton label (6, 5, 4, 3, 2, 1, 0, -1, ......, -6)
+C for (t, b, c, s, d, u, g, u_bar, ..., t_bar)
+
+C X, Q are the usual x, Q;
+C Irt is a return error code (see individual modules for explanation).
+C
+C ---------------------------------------------
+C --> QCD parameters for parton distribution set Iset can be obtained inside
+C the user's program by:
+C Dum = PrCtq2p
+C > (Iset, Iord, Ischeme, MxFlv,
+C > Alam4, Alam5, Alam6, Amas4, Amas5, Amas6,
+C > Xmin, Qini, Qmax, ExpNor)
+C where all but the first argument are output parameters.
+C They should be self-explanatory -- see details under ENTRY PrCtq2p.
+
+C Since the QCD Lambda value for the various sets are needed more often than
+C the other parameters in most applications, a special function
+C Wlamd2p (Iset, Iorder, Neff) is provided
+C which returns the lambda value for Neff = 4,5,6 effective flavors as well as
+C the order these values pertain to.
+
+C ----------------------------------------------
+C The range of (x, Q) used in this round of global analysis is, approxi-
+C mately, 0.01 < x < 0.75 ; and 4 GeV^2 < Q^2 < 400 GeV^2 for fixed target
+C experiments and 0.0001 < x < 0.01 from first official data of HERA.
+
+C The range of (x, Q) used in the reparametrization of the QCD evolved
+C parton distributions is 10E-5 < x < 1 ; 1.6 GeV < Q < 1 TeV. The
+C functional form of this parametrization is:
+
+C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5
+
+C with the A'coefficients being smooth functions of Q. For heavy quarks,
+C a threshold factor is applied to A0 which simulates the proper Q-dependence
+C of the QCD evolution in that region according to the renormalization
+C scheme defined in Collins-Tung, Nucl. Phys. B278, 934 (1986).
+
+C Since this function is positive definite and smooth, it provides sensible
+C extrapolations of the parton distributions if they are called beyond
+C the original range in an application. There is no artificial boundaries
+C or sharp cutoff's.
+C ------------------------------------------------
+
+ FUNCTION Ctq2pPf (Iset, Iparton, X, Q, Irt)
+
+C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton
+C --- the PROBABILITY density
+
+C (Iset, Iparton, X, Q): explained above;
+
+C Irt : return error code: see module Ctq2pPd for explanation.
+
+C IMPLICIT DOUBLE PRECISION (A-H, O-Z)
+C+SEQ, IMPDP.
+
+ Ifl = Iparton
+ JFL = ABS(Ifl)
+C Valence
+ IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN
+ VL = Ctq2pPd (Iset, Ifl, X, Q, Irt)
+ ELSE
+ VL = 0.
+ ENDIF
+C Sea
+ SEA = Ctq2pPd (Iset, -JFL, X, Q, Irt)
+C Full (probability) Distribution
+ Ctq2pPf = (VL + SEA) / X
+
+ Return
+C *************************
+ END
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