subroutine quad(zn)
c---------------------------------------------------------------------------
      save
c
      include 'param_sz.h'
      include 'constcom.h'
      include 'pcordcom.h'
      include 'syscom.h'
      include 'ucom.h'
c
      dimension e(6)
c--------------------------------------------------------------------------
c*
      ne=rne
      sl=zn-z
      k=1
      l=4
      xp=bgx/bgz
      yp=bgy/bgz
      con=1.+xp**2+yp**2
      z=zn
      caysq=el(4,ne)/(brhof*bgz)
      cay=sqrt(abs(caysq))
      if(caysq)10,30,20
   10 continue
      k=4
      l=1
   20 continue
      cayl=cay*sl
      s=sin(cayl)
      c=cos(cayl)
      sh=sinh(cayl)
      ch=cosh(cayl)
      e(k)=c
      e(k+1)=s/cay
      e(k+2)=-cay*s
      e(l)=ch
      e(l+1)=sh/cay
      e(l+2)=cay*sh
      xs=x
      ys=y
      x=e(1)*xs+e(2)*xp
      xp=e(3)*xs+e(1)*xp
      y=e(4)*ys+e(5)*yp
      yp=e(6)*ys+e(4)*yp
      bgx=xp*bgz
      bgy=yp*bgz
      bgz=bgz*sqrt(con/(1.+xp**2+yp**2))
      return
   30 continue
      x=x+xp*sl
      y=y+yp*sl
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*