PETSc version 3.17.4
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# DMComputeL2GradientDiff

This function computes the L_2 difference between the gradient of a function u and an FEM interpolant solution grad u_h.

### Synopsis

    #include "petscdm.h"
    #include "petscdmlabel.h"
    #include "petscds.h"
    PetscErrorCode DMComputeL2GradientDiff(DM dm, PetscReal time, PetscErrorCode (**funcs)(PetscInt, PetscReal, const PetscReal [], const PetscReal[], PetscInt, PetscScalar *, void *), void **ctxs, Vec X, const PetscReal n[], PetscReal *diff)

Collective on dm

### Input Parameters

| dm | - The DM , time - The time
| funcs | - The gradient functions to evaluate for each field component
| ctxs | - Optional array of contexts to pass to each function, or NULL.
| X | - The coefficient vector u_h, a global vector
| n | - The vector to project along

### Output Parameter

| diff | - The diff ||(grad u - grad u_h) . n||_2

### See Also

DMProjectFunction(), DMComputeL2Diff()

### Level

developer

### Location

src/dm/interface/dm.c

### Implementations

DMComputeL2GradientDiff_Plex(DM dm, PetscReal time, PetscErrorCode (**funcs) in src/dm/impls/plex/plexfem.c
Index of all DM routines
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