:orphan:
# PCCompositeType
Determines how two or more preconditioner are composed with the `PCType` of `PCCOMPOSITE` 
## Synopsis
```
typedef enum {
  PC_COMPOSITE_ADDITIVE,
  PC_COMPOSITE_MULTIPLICATIVE,
  PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE,
  PC_COMPOSITE_SPECIAL,
  PC_COMPOSITE_SCHUR,
  PC_COMPOSITE_GKB
} PCCompositeType;
```

## Values

- ***`PC_COMPOSITE_ADDITIVE` -*** results from application of all preconditioners are added together
- ***`PC_COMPOSITE_MULTIPLICATIVE` -*** preconditioners are applied sequentially to the residual freshly
computed after the previous preconditioner application
- ***`PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE` -*** preconditioners are applied sequentially to the residual freshly
computed from first preconditioner to last and then back (Use only for symmetric matrices and preconditioners)
- ***`PC_COMPOSITE_SPECIAL` -*** This is very special for a matrix of the form alpha I + R + S
where first preconditioner is built from alpha I + S and second from
alpha I + R
- ***`PC_COMPOSITE_SCHUR` -*** composes the Schur complement of the matrix from two blocks, see `PCFIELDSPLIT`
- ***`PC_COMPOSITE_GKB` -*** the generalized Golub-Kahan bidiagonalization preconditioner, see `PCFIELDSPLIT`





## See Also
 [](sec_pc), `PCCOMPOSITE`, `PCFIELDSPLIT`, `PC`, `PCCompositeSetType()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petscpctypes.h.html#PCCompositeType">include/petscpctypes.h</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex4.c.html">src/dm/impls/stag/tutorials/ex4.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex60.c.html">src/ksp/ksp/tutorials/ex60.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex71.c.html">src/ksp/ksp/tutorials/ex71.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/include/petscpctypes.h)


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