subroutine plot(xp,yp,chr)
*                ====
*     Line plotting in PostScript
*     ---------------------------
      character chr*1,fmt*16
      external log10
      data ix,iy / 0,0 /
* ... Origin & scaling:
      data xorig,yorig / 0.05,0.05 /
      data fps / 18000. /
*
      ixv=ixp
      iyv=iyp
* ... Move with pen up:
      ixp=fps*(xp+xorig)
      iyp=fps*(yp+yorig)
* ... Draw with pen down:
      if(chr.eq.'d') then
      ix=ixp-ixv
      iy=iyp-iyv
      else
      ix=ixp
      iy=iyp
      endif
* ... Variable format:
      write(fmt,1)
     )      '(i',log10(ix),',a1,i',log10(iy),',a1,a1)'
1     format(a2 ,      i1 ,  a5   ,      i1 ,   a7  )
      write(7,fmt) ix,' ',iy,' ',chr
      return
      end