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# KSPFBCGS
Implements the flexible BiCGStab method. [](sec_flexibleksp) 


## Notes
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.

`KSPFBCGSR` provides another variant of this algorithm that requires fewer `MPI_Allreduce()` calls and my converge faster

See `KSPPIPEBCGS` for a pipelined version of the algorithm

Only supportst right preconditioning


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

## Level
beginner

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


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