subroutine scwall (r,z,er,ez)
c---calculate electric field components due to image
c---charges on wall caused by a ring of charge at z
c---having a radius r
c---having a radius r (only valid for r.le.0.9*rwall).
c---------------------------------------------------------------------------
      save
c
      include 'constcom.h'
      include 'fldcom.h'
      include 'ucom.h'
c
      common/splwall/ rr(10),s(8),sig(8,10),sx(8,10),
     *                sy(8,10),sxy(8,10)
      r1=rp
      z1=zp
c--------------------------------------------------------------------------
c*
      if (r1.lt.rwall) go to 10
      if (r1.eq.rwall) go to 3
c---inside wall.  set field to zero.
      er=0.
      ez=0.
      return
c---calculate fields on wall
    3 continue
      rx=r/rwall
      sr=abs((z1-z)/rwall)
      sg=0.
c---calculate charge density on wall if sr.lt.4.
      if (sr.lt.4.) sg=spl2d2 (rx,sr,10,rr,8,s,sig,sx,sy,sxy,8,0,0)
      ez=0.
      er=-sg/(twopi*rwall**2)
      return
   10 continue
      rx=r/rwall
      ersum=0.
      ezsum=0.
         do 20 n=1,7
c---calculate mid point between knots of spline.
         sb=.5*(s(n)+s(n+1))
c---calculate charge density at mid point
         sg=spl2d2(rx,sb,10,rr,8,s,sig,sx,sy,sxy,8,0,0)
c---calculate total charge on segment
          q=sg*(s(n+1)-s(n))
c---calculate field components due to charged rings
         call fldring (r1,z1,rwall,z+sb*rwall,er1,ez1)
         call fldring (r1,z1,rwall,z-sb*rwall,er2,ez2)
c---sum up fields due to all rings.
         ersum=ersum+q*(er1+er2)
         ezsum=ezsum+q*(ez1+ez2)
   20    continue
      er=ersum
      ez=ezsum
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*