# MatCreateH2OpusFromKernel
Creates a `MATH2OPUS` from a user-supplied kernel. 
## Synopsis
```
PetscErrorCode MatCreateH2OpusFromKernel(MPI_Comm comm, PetscInt m, PetscInt n, PetscInt M, PetscInt N, PetscInt spacedim, const PetscReal coords[], PetscBool cdist, MatH2OpusKernel kernel, void *kernelctx, PetscReal eta, PetscInt leafsize, PetscInt basisord, Mat *nA)
```

## Input Parameters

- ***comm -*** MPI communicator
- ***m -*** number of local rows (or `PETSC_DECIDE` to have calculated if M is given)
- ***n -*** number of local columns (or `PETSC_DECIDE` to have calculated if N is given)
- ***M -*** number of global rows (or `PETSC_DETERMINE` to have calculated if m is given)
- ***N -*** number of global columns (or `PETSC_DETERMINE` to have calculated if n is given)
- ***spacedim -*** dimension of the space coordinates
- ***coords -*** coordinates of the points
- ***cdist -*** whether or not coordinates are distributed
- ***kernel -*** computational kernel (or NULL)
- ***kernelctx -*** kernel context
- ***eta -*** admissibility condition tolerance
- ***leafsize -*** leaf size in cluster tree
- ***basisord -*** approximation order for Chebychev interpolation of low-rank blocks



## Output Parameter

- ***nA -*** matrix



## Options Database Keys

- ***-mat_h2opus_leafsize <`PetscInt`> -*** Leaf size of cluster tree
- ***-mat_h2opus_eta <`PetscReal`> -*** Admissibility condition tolerance
- ***-mat_h2opus_order <`PetscInt`> -*** Chebychev approximation order
- ***-mat_h2opus_normsamples <`PetscInt`> -*** Maximum number of samples to be used when estimating norms





## See Also
 `MatCreate()`, `MATH2OPUS`, `MatCreateH2OpusFromMat()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/h2opus/cuda/math2opus.cu.html#MatCreateH2OpusFromKernel">src/mat/impls/h2opus/cuda/math2opus.cu</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex21.c.html">src/ksp/ksp/tutorials/ex21.c.html</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/impls/h2opus/cuda/math2opus.cu)


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