# 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} PCCompositeType;

     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 preconditions)

     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

### See Also

PCCompositeSetType()

Level:beginner
Location:src/ksp/pc/../../../include/petscpc.h
Index of all PC routines
Table of Contents for all manual pages
Index of all manual pages