An electrical analog is described for the study of reactors whose nuclear properties vary with radius. Several neutron velocity groups can be used. The reactor is divided in uniform homogeneous regions which may be either slabs, spherical shells, or cylindrical shells. The group parameters may be independently varied in these regions and the analog immediately obtains the reactivity. The analog also yields the space distribution of the various neutron groups after being adjusted to the critical condition. A commercial, general purpose analog computer has been adapted to this problem. The analog can also solve the adjoint diffusion equations.