采用CG法求解稀疏不对称的Ax=b-Implementation of a conjugate-gradient type method for solving sparse linear equations and sparse least-squares problems:

Solve Ax = b

or minimize || Ax- b ||2

or minimize || Ax- b ||2+ d2 ||x||2.

The matrix A may be square or rectangular (over-determined or under-determined), and may have any rank. It is represented by a routine for computing Av and A u for given vectors v and u.