The BiConjugate Gradient Stabilized method (Bi-CGSTAB) was developed to
solve nonsymmetric linear systems while avoiding the often irregular
convergence patterns of the Conjugate
Gradient Squared
method (see Van der Vorst [207]). Instead of computing
the CGS sequence
, Bi-CGSTAB computes 
where 
is an 
th degree polynomial describing a steepest
descent update.
Figure: The Preconditioned BiConjugate Gradient Stabilized Method