   mesh
    rectilinear
      nx = 4
      ny = 4
      nz = 4
      bx =  3
      by =  3
      bz =  3
      gmin = -1.0 -1.0 -1.0
      gmax =  1.0  1.0  1.0
    end
    user defined element density, J
     "
     field = 1.0+3.*exp(-1.*(coord));
     field = 2.0+sin(coord*6.0);
     "
    end
   set assign
        nodeset,ihi,1
        nodeset,jhi,2
        nodeset,ilo,3
        nodeset,jlo,4
        sideset,ihi,10
        sideset,jhi,20
        sideset,ilo,30
        sideset,jlo,40
    end
  end

