  The Hartree-Fock-Bogoliubov equation for the ground states of even-even
atomic nuclei is solved using the canonical representation in the coordinate
space for zero range interactions like the Skyrme force. The gradient method is
improved for faster convergence to the solutions under constraint of
orthogonality between canonical orbitals. Necessity of the cut-off of the
pairing interaction is shown even when the number of the canonical orbitals are
restricted. A repulsive dependence of the interaction on the pairing density is
introduced as an implementation of the cut-off which leaves the HFB super
matrix state-independent.
