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# 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.



## See Also
 [](ch_ksp), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPTFQMR`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/tcqmr/tcqmr.c.html#KSPTCQMR">src/ksp/ksp/impls/tcqmr/tcqmr.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/ksp/impls/tcqmr/tcqmr.c)


[Index of all KSP routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)