# KSPTCQMR#

A variant of QMR (quasi minimal residual) [1]

## Notes#

Supports either left or right preconditioning, but not symmetric

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.

## References#

• [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.

KSP: Linear System Solvers, KSPCreate(), KSPSetType(), KSPType, KSP, KSPTFQMR