mrseb.F

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*72*********************************************************************
      SUBROUTINE mrseb
     &                  (x,scale,mode,upv,dnv,usea,dsea,str,chm,bot,glu)
C***************************************************************C
C               C
C     This is a package for the new MRS(A prime,G) parton       C
C     distributions. The minimum Q^2  value is 5 GeV^2 and the  C
C     x range is, as before 10^-5 < x < 1. MSbar factorization  C
C     is used. The package reads 2 grids, which are in separate C
C     files (A prime=for020.dat/ftn20, G=for021.dat/ftn21).     C  
C     Note that x times the parton distribution is returned,    C
C     Q is the scale in GeV,                                    C
C     and Lambda(MSbar,nf=4) = 231/255 MeV for A prime/G.       C
C               C
C MODE=20 for MRS(A prime)                                C
C MODE=21 for MRS(G)                                      C
C               C
C         The reference is :                                    C
C         A.D. Martin, R.G. Roberts and W.J. Stirling,          C
C         Phys. Lett. B354 (1995) 155-162                       C
C                                                               C
C         Comments to : W.J.Stirling@durham.ac.uk               C
C                                                               C
C             >>>>>>>>  CROSS CHECK  <<<<<<<<                   C
C                                                               C
C         THE FIRST NUMBER IN THE 20 GRID IS 0.00341            C
C         THE FIRST NUMBER IN THE 21 GRID IS 0.00269            C
C                                                               C
C         HI: changed SCALE to Q^2                              C
C***************************************************************C
      IMPLICIT REAL*8(a-h,o-z)
      DATA icount /0/
*
* to avoid variable conflictions, a second keep element is necessary
* with the same common block name (see LEPTO2)
*

      COMMON /leptou/ cut(14),lst(40),parl(30),
     &                xlp,ylp,w2lp,q2lp,ulp
      REAL cut,parl,xlp,ylp,w2lp,q2lp,ulp
      INTEGER lst
      SAVE /leptou/

      q2=scale
*     Q2STA= .5D0
      q2sta = .625d0
      q2fin = 1310720.d0
      xmin = 1d-5
      xmax = 1d0

      if (q2.lt.q2sta) then
         q2=q2sta
         IF(cut(5).lt.q2.and.cut(6).gt.q2.AND.icount.lt.10) THEN
            icount = icount + 1
         WRITE(*,*) 'WARNING : MRSEB : Q^2 set to minimal value !',q2
         ENDIF   
      endif
      if (q2.gt.q2fin) then
         q2=q2fin
         IF(cut(5).lt.q2.and.cut(6).gt.q2.AND.icount.lt.10) THEN
            icount = icount + 1
         WRITE(*,*) 'WARNING : MRSEB : Q^2 set to maximal value !',q2
         ENDIF
      endif
      if (x.lt.xmin) then
         x=xmin
         IF(cut(1).lt.x.and.cut(2).gt.x.AND.icount.lt.10) THEN
            icount = icount + 1
         WRITE(*,*) 'WARNING : MRSEB : X set to minimal value !',x
         ENDIF   
      endif
      if (x.gt.xmax) then
         x=xmax
         IF(cut(1).lt.x.and.cut(2).gt.x.AND.icount.lt.10) THEN
            icount = icount + 1
         WRITE(*,*) 'WARNING : MRSEB : X set to maximal value !',x
         ENDIF         
      endif

      IF(mode.EQ.20) 
     .   CALL strc20(x,scale,upv,dnv,usea,dsea,str,chm,bot,glu)
      IF(mode.EQ.21) 
     .   CALL strc21(x,scale,upv,dnv,usea,dsea,str,chm,bot,glu)
      IF(mode.EQ.10) THEN 
         IF(q2.LT.0.625d0.OR.q2.GT.1310720.d0) print 99
      IF(q2.GT.5d0) CALL strc10(x,scale,upv,dnv,usea,dsea,str,chm,bot,
     x        glu)
      IF(q2.LE.5d0) CALL strc11(x,scale,upv,dnv,usea,dsea,str,chm,bot,
     x        glu)
 99      FORMAT('  WARNING:  Q^2 VALUE IS OUT OF RANGE   ')
      ENDIF
*  check for positive definiteness

      IF(upv.LT.0.0) upv=0.0
      IF(dnv.LT.0.0) dnv=0.0
      IF(usea.LT.0.0) usea=0.0
      IF(dsea.LT.0.0) dsea=0.0
      IF(glu.LT.0.0) glu=0.0
      IF(str.LT.0.0) str=0.0
      IF(chm.LT.0.0) chm=0.0
      IF(bot.LT.0.0) bot=0.0

      RETURN
      END