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# PetscDualSpaceApplyFVM
Apply a functional from the dual space basis to an input function by assuming a point evaluation functional at the cell centroid. 
## Synopsis
```
#include "petscfe.h" 
PetscErrorCode PetscDualSpaceApplyFVM(PetscDualSpace sp, PetscInt f, PetscReal time, PetscFVCellGeom *cgeom, PetscInt Nc, PetscErrorCode (*func)(PetscInt, PetscReal, const PetscReal[], PetscInt, PetscScalar *, void *), void *ctx, PetscScalar *value)
```

## Input Parameters

- ***sp    -*** The `PetscDualSpace` object
- ***f     -*** The basis functional index
- ***time  -*** The time
- ***cgeom -*** A context with geometric information for this cell, we currently just use the centroid
- ***Nc    -*** The number of components for the function
- ***func  -*** The input function
- ***ctx   -*** A context for the function



## Output Parameter

- ***value -*** The output value (scalar)



## Calling Sequence of `func`
```none
  PetscErrorCode func(PetscInt dim, PetscReal time, const PetscReal x[], PetscInt numComponents, PetscScalar values[], void *ctx)
```





## Note
The idea is to evaluate the functional as an integral $ n(f) = \int dx n(x) . f(x)$ where both n and f have Nc components.


## See Also
 `PetscDualSpace`, `PetscDualSpaceCreate()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/dt/dualspace/interface/dualspace.c.html#PetscDualSpaceApplyFVM">src/dm/dt/dualspace/interface/dualspace.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/dm/dt/dualspace/interface/dualspace.c)


[Index of all DUALSPACE routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)