# PCHYPRE
Allows you to use the matrix element based preconditioners in the LLNL package hypre as PETSc `PC` 
## Options Database Keys

- ***-pc_hypre_type -*** One of euclid, pilut, parasails, boomeramg, ams, ads
- ***-pc_hypre_boomeramg_nodal_coarsen <n> -*** where n is from 1 to 6 (see `HYPRE_BOOMERAMGSetNodal()`)
- ***-pc_hypre_boomeramg_vec_interp_variant <v> -*** where v is from 1 to 3 (see `HYPRE_BoomerAMGSetInterpVecVariant()`)
- ***Many others, run with -*** pc_type hypre -pc_hypre_type XXX -help to see options for the XXX preconditioner





## Notes
Apart from pc_hypre_type (for which there is `PCHYPRESetType()`),
the many hypre options can ONLY be set via the options database (e.g. the command line
or with `PetscOptionsSetValue()`, there are no functions to set them)

The options -pc_hypre_boomeramg_max_iter and -pc_hypre_boomeramg_tol refer to the number of iterations
(V-cycles) and tolerance that boomeramg does EACH time it is called. So for example, if
-pc_hypre_boomeramg_max_iter is set to 2 then 2-V-cycles are being used to define the preconditioner
(-pc_hypre_boomeramg_tol should be set to 0.0 - the default - to strictly use a fixed number of
iterations per hypre call). -ksp_max_it and -ksp_rtol STILL determine the total number of iterations
and tolerance for the Krylov solver. For example, if -pc_hypre_boomeramg_max_iter is 2 and -ksp_max_it is 10
then AT MOST twenty V-cycles of boomeramg will be called.

Note that the option -pc_hypre_boomeramg_relax_type_all defaults to symmetric relaxation
(symmetric-SOR/Jacobi), which is required for Krylov solvers like CG that expect symmetry.
Otherwise, you may want to use -pc_hypre_boomeramg_relax_type_all SOR/Jacobi.
If you wish to use BoomerAMG WITHOUT a Krylov method use -ksp_type richardson NOT -ksp_type preonly
and use -ksp_max_it to control the number of V-cycles.
(see the PETSc FAQ.html at the PETSc website under the Documentation tab).

`MatSetNearNullSpace()` - if you provide a near null space to your matrix it is ignored by hypre UNLESS you also use
the following two options: ``-pc_hypre_boomeramg_nodal_coarsen <n> -pc_hypre_boomeramg_vec_interp_variant <v>``

See `PCPFMG`, `PCSMG`, and `PCSYSPFMG` for access to hypre's other (nonalgebraic) multigrid solvers

For `PCHYPRE` type of ams or ads auxiliary data must be provided to the preconditioner with `PCHYPRESetDiscreteGradient()`,
`PCHYPRESetDiscreteCurl()`, `PCHYPRESetInterpolations()`, `PCHYPRESetAlphaPoissonMatrix()`, `PCHYPRESetBetaPoissonMatrix()`, `PCHYPRESetEdgeConstantVectors()`,
`PCHYPREAMSSetInteriorNodes()`

PETSc provides its own geometric and algebraic multigrid solvers `PCMG` and `PCGAMG`, also see `PCHMG` which is useful for certain multicomponent problems


## GPU Notes
To configure hypre BoomerAMG so that it can utilize NVIDIA GPUs run ./configure --download-hypre --with-cuda
Then pass `VECCUDA` vectors and `MATAIJCUSPARSE` matrices to the solvers and PETSc will automatically utilize hypre's GPU solvers.

To configure hypre BoomerAMG so that it can utilize AMD GPUs run ./configure --download-hypre --with-hip
Then pass `VECHIP` vectors to the solvers and PETSc will automatically utilize hypre's GPU solvers.


## See Also
 `PCCreate()`, `PCSetType()`, `PCType`, `PC`, `PCHYPRESetType()`, `PCPFMG`, `PCGAMG`, `PCSYSPFMG`, `PCSMG`, `PCHYPRESetDiscreteGradient()`,
`PCHYPRESetDiscreteCurl()`, `PCHYPRESetInterpolations()`, `PCHYPRESetAlphaPoissonMatrix()`, `PCHYPRESetBetaPoissonMatrix()`, `PCHYPRESetEdgeConstantVectors()`,
PCHYPREAMSSetInteriorNodes()

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/hypre/hypre.c.html#PCHYPRE">src/ksp/pc/impls/hypre/hypre.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/hypre/hypre.c)


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