  In topology optimization, the design parameter with no contribution to the
objective function vanishes. This causes the stiffness matrix to become
singular. We show that a local optimal solution is obtained by Conjugate
Residual Method and Conjugate Gradient Method even if the stiffness matrix
becomes singular. We prove that CGMconverges to a local optimal solution in
that case. Computer simulation shows that CGM gives the same solutions obtained
by CRM in case of a cantilever beam problem.
