db/d9c/pypcmp_8f_source.html

C*********************************************************************


C...PYPCMP: Auxiliary to PYPDFU.

C...Giving the momentum integral of a companion quark, with its

C...partner at XS, using an approximate gluon density like (1-x)^NPOW/x.

C...The value corresponds to an unrescaled range between 0 and 1-XS.


      FUNCTION pypcmp(XS,NPOW)

      IMPLICIT NONE

      DOUBLE PRECISION xs, pypcmp

      INTEGER npow

      IF (xs.GE.1d0.OR.xs.LE.0d0) THEN

        pypcmp=0d0

      ELSEIF (npow.LE.0) THEN

        pypcmp=xs*(5d0+xs*(-9d0-2d0*xs*(-3d0+xs))+3d0*log(xs))

        pypcmp=pypcmp/((-1d0+xs)*(2d0+xs*(-1d0+2d0*xs)))

      ELSEIF (npow.EQ.1) THEN

        pypcmp=-1d0-3d0*xs+(2d0*(-1d0+xs)**2*(1d0+xs+xs**2))

     &       /(2d0+xs**2*(xs-3d0)+3d0*xs*log(xs))

      ELSEIF (npow.EQ.2) THEN

        pypcmp=xs*((1d0-xs)*(19d0+xs*(43d0+4d0*xs))

     &       +6d0*log(xs)*(1d0+6d0*xs+4d0*xs**2))

        pypcmp=pypcmp/(4d0*((xs-1d0)*(1d0+xs*(4d0+xs))

     &       -3d0*xs*log(xs)*(1+xs)))

      ELSEIF (npow.EQ.3) THEN

        pypcmp=3d0*xs*((xs-1)*(7d0+xs*(28d0+13d0*xs))

     &       -2d0*log(xs)*(1d0+xs*(9d0+2d0*xs*(6d0+xs))))

        pypcmp=pypcmp/(4d0+27d0*xs-31d0*xs**3

     &       +6d0*xs*log(xs)*(3d0+2d0*xs*(3d0+xs)))

      ELSE

        pypcmp=(-9d0*xs*(xs**2-1d0)*(5d0+xs*(24d0+xs))+12d0*xs*log(xs)

     &       *(1d0+2d0*xs)*(1d0+2d0*xs*(5d0+2d0*xs)))

        pypcmp=pypcmp/(8d0*(1d0+2d0*xs)*((xs-1d0)*(1d0+xs*(10d0+xs))

     &       -6d0*xs*log(xs)*(1d0+xs)))

      ENDIF

      RETURN

      END