| see KSPSolve() |
The "residual norm" computed in this algorithm is actually just an upper bound on the actual residual norm. That is for left preconditioning it is a bound on the preconditioned residual and for right preconditioning it is a bound on the true residual.
| 1. | - Tony F. Chan, Lisette de Pillis, and Henk van der Vorst, Transpose free formulations of Lanczos type methods for nonsymmetric linear systems, Numerical Algorithms, Volume 17, 1998. |