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# PCFieldSplitGetSubKSP
Gets the `KSP` contexts for all splits 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCFieldSplitGetSubKSP(PC pc, PetscInt *n, KSP *subksp[])
```
Collective


## Input Parameter

- ***pc -*** the preconditioner context



## Output Parameters

- ***n -*** the number of splits
- ***subksp -*** the array of `KSP` contexts





## Notes
After `PCFieldSplitGetSubKSP()` the array of `KSP`s is to be freed by the user with `PetscFree()`
(not the `KSP`, just the array that contains them).

You must call `PCSetUp()` before calling `PCFieldSplitGetSubKSP()`.

If the fieldsplit is of type `PC_COMPOSITE_SCHUR`, it returns the `KSP` object used inside the
Schur complement and the `KSP` object used to iterate over the Schur complement.
To access all the `KSP` objects used in `PC_COMPOSITE_SCHUR`, use `PCFieldSplitSchurGetSubKSP()`.

If the fieldsplit is of type `PC_COMPOSITE_GKB`, it returns the `KSP` object used to solve the
inner linear system defined by the matrix H in each loop.


## Fortran Usage
You must pass in a `KSP` array that is large enough to contain all the `KSP`s.
You can call `PCFieldSplitGetSubKSP`(pc,n,`PETSC_NULL_KSP`,ierr) to determine how large the
`KSP` array must be.


## Developer Note
There should be a `PCFieldSplitRestoreSubKSP()` instead of requiring the user to call `PetscFree()`

The Fortran interface should be modernized to return directly the array of values.


## See Also
  [](sec_block_matrices), `PC`, `PCFIELDSPLIT`, `PCFieldSplitSetFields()`, `PCFieldSplitSetIS()`, `PCFieldSplitSchurGetSubKSP()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitGetSubKSP">src/ksp/pc/impls/fieldsplit/fieldsplit.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex43.c.html">src/ksp/ksp/tutorials/ex43.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex70.c.html">src/ksp/ksp/tutorials/ex70.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex70.c.html">src/snes/tutorials/ex70.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitGetSubKSP_FieldSplit">PCFieldSplitGetSubKSP_FieldSplit in src/ksp/pc/impls/fieldsplit/fieldsplit.c</A><BR>


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


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