In the linear system Ax = b the points x are sometimes constrained to lie in a given subspace S of column space ofA. Drazin inverse for any singular or nonsingular matrix, exist and is unique. In this paper, the singular consistent or inconsistent constrained linear systems are introduced and the effect of Drazin inverse in solving such systems is investigated. Constrained linear system arise in electrical network theory. پرونده مقاله