# PCCompositeType
Determines how two or more preconditioner are composed 
## Synopsis
```
typedef enum {
  PC_COMPOSITE_ADDITIVE,
  PC_COMPOSITE_MULTIPLICATIVE,
  PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE,
  PC_COMPOSITE_SPECIAL,
  PC_COMPOSITE_SCHUR,
  PC_COMPOSITE_GKB
} PCCompositeType;
```
```none
`PC_COMPOSITE_ADDITIVE` - results from application of all preconditioners are added together
```
```none
`PC_COMPOSITE_MULTIPLICATIVE` - preconditioners are applied sequentially to the residual freshly
```
```none
computed after the previous preconditioner application
```
```none
`PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE` - preconditioners are applied sequentially to the residual freshly
```
```none
computed from first preconditioner to last and then back (Use only for symmetric matrices and preconditioners)
```
```none
`PC_COMPOSITE_SPECIAL` - This is very special for a matrix of the form alpha I + R + S
```
```none
where first preconditioner is built from alpha I + S and second from
```
```none
alpha I + R
```




## See Also
 `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.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex60.c.html">src/ksp/ksp/tutorials/ex60.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex71.c.html">src/ksp/ksp/tutorials/ex71.c.html</A><BR>


---
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[Index of all PC routines](index.md)  
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[Index of all manual pages](/docs/manualpages/singleindex.md)  
