subroutine poisson(filepois,zoffset,rmult)
c-----------------------------------------------------------------------
c
      include 'param_sz.h'
      include 'flagcom.h'
      include 'pfieldcom.h'
      include 'ucom.h'
c
      character filepois*256 ! dimension modifiee glm (avant : 12)
c-----------------------------------------------------------------------
      print *, ' poisson recoit : ', filepois
      nlast = index(filepois, ' ')
      if (nlast .eq. 0) nlast = len(filepois) + 1
c      open(unit=npois,file=filepois//'.psfld',err=200,status='old')
      open(unit=npois,file=filepois(1:nlast-1)//'.psfld',err=200,
     1  status='old')
      read(npois,*) prmin,prmax,nrp
      read(npois,*) pzmin,pzmax,nzp
C      print *, ' lu prmin, max, nrp ', prmin,prmax,nrp
C      print *, ' lu pzmin,pzmax,nzp ', pzmin,pzmax,nzp


      pdr=(prmax-prmin)/float(nrp)
      pdz=(pzmax-pzmin)/float(nzp)
      do 20 k=0,nrp-1
      do 30 l=0,nzp-1
      read(npois,fmt=*,err=201) rbfld(k,l),zbfld(k,l)
  30  continue
  20  continue
      close(npois)
      pzmin=pzmin+zoffset
      pzmax=pzmax+zoffset
      if(rmult.ne.1.)then
      do 10 k=0,nrp-1
      do 10 l=0,nzp-1
      rbfld(k,l)=rbfld(k,l)*rmult
      zbfld(k,l)=zbfld(k,l)*rmult
  10  continue
      endif
      poiflag=.true.
      return
 200  write(nnout,*)' error opening ',filepois,' in Poisson'
      return
 201  write(nnout,*)' error reading ',filepois,' in Poisson'
      return
      end
c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*