Conjugate gradient squared method

In numerical linear algebra, the conjugate gradient squared method (CGS) is an iterative algorithm for solving systems of linear equations of the form ${\displaystyle A{\mathbf {x}}={\mathbf {b}}}$, particularly in cases where computing the transpose ${\displaystyle A^{T}}$ is impractical. The CGS method was developed as an improvement to the biconjugate gradient method.