:orphan:
# DMDAVecGetKokkosOffsetViewDOF
Gets a Kokkos OffsetView that contains up-to-date data of a vector in the given memory space, with DOF as the rightest dimension of the OffsetView 
## Synopsis
```
template <class MemorySpace>
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM, Vec, Kokkos::Experimental::OffsetView<const PetscScalar **, Kokkos::LayoutRight, MemorySpace> *)
```

## Synopsis
```
#include <petscdmda_kokkos.hpp>
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<const PetscScalar**,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar**,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOFWrite(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar**,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<const PetscScalar***,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar***,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOFWrite(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar***,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<const PetscScalar****,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOF(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar****,Kokkos::LayoutRight,MemorySpace>* kv);
PetscErrorCode DMDAVecGetKokkosOffsetViewDOFWrite(DM da,Vec v,Kokkos::Experimental::OffsetView<PetscScalar****,Kokkos::LayoutRight,MemorySpace>* kv);
```

Logically Collective


## Input Parameters

- ***da -*** the distributed array
- ***v -*** the vector, either a vector the same size as one obtained with `DMCreateGlobalVector()` or `DMCreateLocalVector()`



## Output Parameter

- ***kv -*** the Kokkos OffsetView with a user-specified template parameter MemorySpace



## Notes
Call `DMDAVecRestoreKokkosOffsetViewDOF()` or `DMDAVecRestoreKokkosOffsetViewDOFWrite()` once you have finished accessing the OffsetView.

If the vector is not a `VECKOKKOS` an error will be raised.

If the vector is a local vector (obtained with `DMCreateLocalVector()` etc) then the ghost point locations are accessible. If it is
a global vector then the ghost points are not accessible. Of course with the local vector you will have to do the
appropriate `DMGlobalToLocalBegin()` and `DMGlobalToLocalEnd()` to have correct values in the ghost locations.

These routines are similar to `DMDAVecGetArrayDOF()` and friends. One can read-only, write-only or read/write access the returned
Kokkos OffsetView.  Note that passing in a constant OffsetView enables read-only access.
Currently, only two memory spaces are supported: Kokkos::HostSpace and Kokkos::DefaultExecutionSpace::memory_space.
If needed, a memory copy will be internally called to copy the latest vector data to the given memory space.

In C, to access the returned array of `DMDAVecGetArrayDOF()`, the indexing is "backwards", i.e., array[k][j][i][c] (instead of array[c][i][j][k]),
where i, j, k are loop variables for the x, y, z dimensions respectively, and c is the loop variable for DOFs, as specified in `DMDACreate3d()`,
for example.

To give users the same experience as `DMDAVecGetArrayDOF()`, we mandate the returned OffsetView always has Kokkos::LayoutRight (that is, rightest
subscript has a stride 1, as in C multi-dimensional arrays), regardless of whether the memory space is host or device. Thus it is important
to use Iterate::Right as IterateInner if one uses Kokkos::MDRangePolicy to access the OffsetView.

Note that for a 3D `DMDA`, the OffsetView kv's first dimension (i.e., the leftest, dim 0) corresponds to DMDA's z direction, and its second-to-last dimension
(rightest) corresponds to DMDA's x direction.

If the vector is a global vector, we have
```none
      kv.extent(0) = zm,  kv.begin(0) = zs, kv.end(0) = zs+zm
      kv.extent(1) = ym,  kv.begin(1) = ys, kv.end(1) = ys+ym
      kv.extent(2) = xm,  kv.begin(2) = xs, kv.end(2) = xs+xm
      kv.extent(3) = dof, kv.begin(3) = 0,  kv.end(3) = dof
```

If the vector is a local vector, we have
```none
      kv.extent(0) = gzm, kv.begin(0) = gzs, kv.end(0) = gzs+gzm
      kv.extent(1) = gym, kv.begin(1) = gys, kv.end(1) = gys+gym
      kv.extent(2) = gxm, kv.begin(2) = gxs, kv.end(2) = gxs+gxm
      kv.extent(3) = dof, kv.begin(3) = 0,   kv.end(3) = dof
```


The starts and widths above are obtained by
```none
     DMDAGetCorners(da,&xs,&ys,&zs,&xm,&ym,&zm);
     DMDAGetGhostCorners(da,&gxs,&gys,&gzs,&gxm,&gym,&gzm);
```


For example, to initialize a grid,
```none
    typedef Kokkos::Experimental::OffsetView<const PetscScalar****,Kokkos::LayoutRight,MemorySpace> PetscScalarKokkosOffsetView4D;

    PetscScalarKokkosOffsetView4D kv;
    DMDAVecGetKokkosOffsetViewDOFWrite(da,v,&kv); // v is a global vector
    DMDAGetCorners(da,&xs,&ys,&zs,&xm,&ym,&zm);

    parallel_for ("Label",MDRangePolicy <Rank<4, Iterate::Right, Iterate::Right>>(
      {zs,ys,xs,0},{zs+zm,ys+ym,xs+xm,dof}), KOKKOS_LAMBDA (PetscInt k,PetscInt j,PetscInt i,PetscInt c) {
      kv(k,j,i,c) = ...;
    });
    DMDAVecRestoreKokkosOffsetViewDOFWrite(da,v,&kv);
```





## See Also
 `DMDAVecRestoreKokkosOffsetViewDOF()`, `DMDAGetGhostCorners()`, `DMDAGetCorners()`, `VecGetArray()`, `VecRestoreArray()`, `DMDAVecRestoreArray()`, `DMDAVecRestoreArrayDOF()`
`DMDAVecGetArrayDOF()`, `DMDAVecGetArrayWrite()`, `DMDAVecRestoreArrayWrite()`, `DMDAVecGetArrayRead()`, `DMDAVecRestoreArrayRead()`,
`DMStagVecGetArray()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petscdmda_kokkos.hpp#DMDAVecGetKokkosOffsetViewDOF">include/petscdmda_kokkos.hpp</A>


---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/include/petscdmda_kokkos.hpp)


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