real function sysclass(x,q,iclass)
**************************************************************************
*     Function to get the compact parametrisations.
*     See  Appendix of the ZEUS 1994 F2 paper DESY 96-076
*     ! These functions are valid only in the kinematic range of !
*     ! of the F2 measurements in the paper !
*
*     IN: real x,q  --> bjorken x and Q^2
*         int. iclass --> class +-1 to +-6
*                         1 = A, 2 = B, etc...
*
*     OUT: sysclass  --> fractional deviation on F2: F2_syst=F2*sysclass,
*                        where F2_syst is systematically offset.
*                                 
*
* Comments to: Vreeswijk@nikhef.nl or Kooijman@nikhef.nl
**************************************************************************

      integer iclass
      real x,q, xx,s,y,ay,aq
*     
*     if input iclass out of range, routine will return
*     sysclass = -1.
*
      sysclass = -200.
*
      xx = x
      s = 4.*27.5*820.
      y = q/(xx*s)
      ay = abs(alog10(y))
      aq = alog10(q)
*
      if(iclass .eq. 1) then
         sysclass = 2.34 - 0.96*aq
      endif
      if(iclass .eq. -1) then
         sysclass = -1.94 + 0.83*aq
      endif
      if(iclass .eq. 2) then
         sysclass = 0.126/(ay**2)
      endif
      if(iclass .eq. -2) then
         sysclass = -0.085/(ay**2)
      endif
      if(iclass .eq. 3) then
         sysclass = 0.153/(ay**2)-0.0044*ay**7
      endif
      if(iclass .eq. -3) then
         sysclass = -0.145/(ay**2)+0.0034*ay**7
      endif
      if(iclass .eq. 4) then
         sysclass = 0.132/(ay**2)+0.0043*ay**7-0.69
      endif
      if(iclass .eq. -4) then
         sysclass = -0.146/(ay**2)-0.0074*ay**7+1.29
      endif
      if(iclass .eq. 5) then
         sysclass = 1.62*(ay**2)-0.39*ay**4
      endif
      if(iclass .eq. -5) then
         sysclass = -3.05*(ay**2)+0.77*ay**4
      endif
      if(iclass .eq. 6) then
         sysclass = -1.05+0.83*ay
      endif
      if(iclass .eq. -6) then
         sysclass = 1.00-0.79*ay
      endif

      sysclass = 1.00 + sysclass/100.
      if (q.gt.100) sysclass=1.
      return
      end