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# PetscFormKey

This key indicates how to use a set of pointwise functions defining part of a system of equations

## Synopsis

    typedef struct {
      DMLabel  label; /* The (label, value) select a subdomain */
      PetscInt value;
      PetscInt field; /* Selects the field for the test function */
      PetscInt part;  /* Selects the equation part. For example, LHS = 0 and RHS = 1 in IMEX methods. More pieces can be present for operator splitting methods. */
    } PetscFormKey;

The subdomain on which to integrate is specified by (label, value), the test function field by (field), and the piece of the equation by (part). For example, LHS = 0 and RHS = 1 in IMEX methods. More pieces can be present for operator splitting methods.

## Note

This is a struct, not a `PetscObject`

## See Also

`DMPlexSNESComputeResidualFEM()`, `DMPlexSNESComputeJacobianFEM()`, `DMPlexSNESComputeBoundaryFEM()`

## Level

intermediate

## Location

include/petscdstypes.h

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