PCCompositeType

Determines how two or more preconditioner are composed

typedef enum {PC_COMPOSITE_ADDITIVE,PC_COMPOSITE_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_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