PETSc version 3.17.4
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# DMSubDomainHookAdd

adds a callback to be run when restricting a problem to the coarse grid

### Synopsis

    #include "petscdm.h"
    #include "petscdmlabel.h"
    #include "petscds.h"
    PetscErrorCode DMSubDomainHookAdd(DM global,PetscErrorCode (*ddhook)(DM,DM,void*),PetscErrorCode (*restricthook)(DM,VecScatter,VecScatter,DM,void*),void *ctx)

Logically Collective on global

### Input Parameters

| global | - global DM
| ddhook | - function to run to pass data to the decomposition DM upon its creation
| restricthook | - function to run to update data on block solve (at the beginning of the block solve)
| ctx | - [optional] user-defined context for provide data for the hooks (may be NULL)

### Calling sequence for ddhook

       ddhook(DM global,DM block,void *ctx)

| global | - global DM
| block | - block DM
| ctx | - optional user-defined function context

### Calling sequence for restricthook

       restricthook(DM global,VecScatter out,VecScatter in,DM block,void *ctx)

| global | - global DM
| out | - scatter to the outer (with ghost and overlap points) block vector
| in | - scatter to block vector values only owned locally
| block | - block DM
| ctx | - optional user-defined function context

### Notes

This function is only needed if auxiliary data needs to be set up on subdomain DMs.

If this function is called multiple times, the hooks will be run in the order they are added.

In order to compose with nonlinear preconditioning without duplicating storage, the hook should be implemented to extract the global information from its context (instead of from the SNES).

This function is currently not available from Fortran.

### See Also

DMRefineHookAdd(), SNESFASGetInterpolation(), SNESFASGetInjection(), PetscObjectCompose(), PetscContainerCreate()

### Level

advanced

### Location

src/dm/interface/dm.c
Index of all DM routines
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Index of all manual pages