: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
include/petscpctypes.h
## Examples
src/dm/impls/stag/tutorials/ex4.c
src/ksp/ksp/tutorials/ex60.c
src/ksp/ksp/tutorials/ex71.c
---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/include/petscpctypes.h)
[Index of all PC routines](index.md)
[Table of Contents for all manual pages](/manualpages/index.md)
[Index of all manual pages](/manualpages/singleindex.md)