anchor.diff:         integer fnc
          logical util_get_io_unit
          external util_get_io_unit
  +       double precision pi
  +c
          pname = "rdf_compute"
  +       pi = acos(-1.0)
   c
   c      ----------------------
   c      compute lattice params
  
positive.code:      $            form='formatted',status='old',err=911)
            read(fnc,*,err=911) ic,ang0,ang1
            close(fnc)
         end if 
  
  c      ----------------------------
  c      construct relative distances
  c      and bin rdf
  
negative.code:              ang = SUM(rd*rd1)/(d1*d)
               ocons = ang.ge.ang0
               ocons = ocons.and.(ang.le.ang1)
             end if
             if(d.gt.0.01) k = int(d/dr)+1
             if(k.le.nb.and.ocons ) then
  