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# KSPFBCGSR
Implements a mathematically equivalent variant of flexible bi-CG-stab, `KSPFBCGS`. [](sec_flexibleksp) 


## Notes
This implementation requires fewer `MPI_Allreduce()` calls than `KSPFBCGS` and may converge faster

See `KSPPIPEBCGS` for a pipelined version of the algorithm

Flexible BiCGStab, unlike most Krylov methods, allows the preconditioner to be nonlinear, that is the action of the preconditioner to a vector need not be linear
in the vector entries.

Only supports right preconditioning


## See Also
 [](ch_ksp),  [](sec_flexibleksp), `KSPFBCGSR`, `KSPPIPEBCGS`, `KSPBCGSL`, `KSPBCGS`, `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPFBCGS`, `KSPSetPCSide()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/bcgs/fbcgsr/fbcgsr.c.html#KSPFBCGSR">src/ksp/ksp/impls/bcgs/fbcgsr/fbcgsr.c</A>


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