source: PSPA/parmelaPSPA/trunk/fldring.f @ 476

      subroutine fldring (r1,z1,r,z,er,ez)
c---compute radial and longitudinal components of
c---electric field at r1,z1 due to ring of charge
c---at z having radius r.
c-----------------------------------------------------------------------
c
      include 'constcom.h'
      include 'ucom.h'
c
c-----------------------------------------------------------------------
c*
      pisq=pi**2
      d=z1-z
      c=(r1-r)**2
      b=(r1+r)**2
      a=4.0*r*r1/(b+d**2)
      call eint (a,ee,ek)
      er=0.0
      a=sqrt(b+d**2)
      if (r1.eq.0.) go to 10
      er=(ek-(r**2-r1**2+d**2)*ee/(c+d**2))/(4.*pisq*r1*a)
   10 continue
      ez=d*ee/(a*(c+d**2)*2.*pisq)
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*