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# DMProjectFieldLabel

This projects the given function of the input fields into the function space provided, putting the coefficients in a global vector, calculating only over the portion of the domain specified by the label.

## Synopsis

    #include "petscdm.h"
    #include "petscdmlabel.h"
    #include "petscds.h"
    PetscErrorCode DMProjectFieldLabel(DM dm, PetscReal time, DMLabel label, PetscInt numIds, const PetscInt ids[], PetscInt Nc, const PetscInt comps[], Vec U, void (**funcs)(PetscInt dim, PetscInt Nf, PetscInt NfAux, const PetscInt uOff[], const PetscInt uOff_x[], const PetscScalar u[], const PetscScalar u_t[], const PetscScalar u_x[], const PetscInt aOff[], const PetscInt aOff_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar a_x[], PetscReal t, const PetscReal x[], PetscInt numConstants, const PetscScalar constants[], PetscScalar f[]), InsertMode mode, Vec X)

Not Collective

## Input Parameters

- dm - The `DM`

- time - The time

- label - The `DMLabel` marking the portion of the domain to output

- numIds - The number of label ids to use

- ids - The label ids to use for marking

- Nc - The number of components to set in the output, or `PETSC_DETERMINE` for all components

- comps - The components to set in the output, or `NULL` for all components

- U - The input field vector

- funcs - The functions to evaluate, one per field

- mode - The insertion mode for values

## Output Parameter

- X - The output vector

## Calling sequence of `funcs`

- dim - The spatial dimension

- Nf - The number of input fields

- NfAux - The number of input auxiliary fields

- uOff - The offset of each field in u[]

- uOff_x - The offset of each field in u_x[]

- u - The field values at this point in space

- u_t - The field time derivative at this point in space (or NULL)

- u_x - The field derivatives at this point in space

- aOff - The offset of each auxiliary field in u[]

- aOff_x - The offset of each auxiliary field in u_x[]

- a - The auxiliary field values at this point in space

- a_t - The auxiliary field time derivative at this point in space (or NULL)

- a_x - The auxiliary field derivatives at this point in space

- t - The current time

- x - The coordinates of this point

- numConstants - The number of constants

- constants - The value of each constant

- f - The value of the function at this point in space

## Note

There are three different `DM`s that potentially interact in this function. The output `DM`, dm, specifies the layout of the values calculates by funcs. The input `DM`, attached to U, may be different. For example, you can input the solution over the full domain, but output over a piece of the boundary, or a subdomain. You can also output a different number of fields than the input, with different discretizations. Last the auxiliary `DM`, attached to the auxiliary field vector, which is attached to dm, can also be different. It can have a different topology, number of fields, and discretizations.

## Developer Notes

This API is specific to only particular usage of `DM`

The notes need to provide some information about what has to be provided to the `DM` to be able to perform the computation.

## See Also

DM Basics, `DM`, `DMProjectField()`, `DMProjectFieldLabelLocal()`, `DMProjectFunction()`, `DMComputeL2Diff()`

## Level

intermediate

## Location

src/dm/interface/dm.c

Index of all DM routines
Table of Contents for all manual pages
Index of all manual pages