[petsc-dev] Julia Petsc Wrapper

Matthew Knepley knepley at gmail.com
Tue Jul 14 12:04:50 CDT 2015

On Tue, Jul 14, 2015 at 10:56 AM, Jared Crean <jcrean01 at gmail.com> wrote:

>      Hello everyone,
>         I got the package in a reasonably working state and Travis testing
> setup, so I am putting the package up on Github.
>         https://github.com/JaredCrean2/PETSc.jl
>         There is still a lot more work to do, but its a start.
>         A couple questions:
>         When looking though the code, I noticed the MPI communicator is
> being passed as a 64 bit integer.  mpi.h typedefs it as an int, so
> shouldn't it be a 32 bit integer?

Some MPI implementations store the communicator as a pointer, which may be
64 bits. I think the only thing the standard says is
that MPI_Comm should be defined.

>         Also, is there a way to find out at runtime what datatype a
> PetscScalar is?  It appears PetscDataTypeGetSize does not accept
> PetscScalar as an argument.

If PETSC_USE_COMPLEX is defined its PETSC_COMPLEX, otherwise its
PETSC_REAL. You can also just use sizeof(PetscScalar). What do you
want to do?



>     Jared Crean
> On 07/06/2015 09:02 AM, Matthew Knepley wrote:
>  On Mon, Jul 6, 2015 at 4:59 AM, Patrick Sanan <patrick.sanan at gmail.com>
> wrote:
>> I had a couple of brief discussions about this at Juliacon as well. I
>> think it would be useful, but there are a couple of things to think about
>> from the start of any new attempt to do this:
>> 1. As Jack pointed out, one issue is that the PETSc library must be
>> compiled for a particular precision. This raises some questions - should
>> several versions of the library be built to allow for flexibility?
>> 2. An issue with wrapping PETSc is always that the flexibility of using
>> the PETSc options paradigm is reduced - how can this be addressed?
>> Could/should an expert user be able to access the options database
>> directly, or would this be too much violence to the wrapper abstraction?
>  I have never understood why this is an issue. Can't you just wrap our
> interface level, and use the options just as we do? That
> is essentially what petsc4py does. What is limiting in this methodology?
> On the other hand, requiring specific types, ala FEniCS,
> is very limiting.
>     Matt
>>  On Sat, Jul 4, 2015 at 11:00 PM, Jared Crean <jcrean01 at gmail.com> wrote:
>>>  Hello,
>>>      I am a graduate student working on a CFD code written in Julia, and
>>> I am interested in using Petsc as a linear solver (and possibly for the
>>> non-linear solves as well) for the code.  I discovered the Julia wrapper
>>> file Petsc.jl in Petsc and have updated it to work with the current version
>>> of Julia and the MPI.jl package, using only MPI for communication (I don't
>>> think Julia's internal parallelism will scale well enough, at least not in
>>> the near future).
>>>      I read the discussion on Github [
>>> https://github.com/JuliaLang/julia/issues/2645], and it looks like
>>> there currently is not a complete package to access Petsc from Julia.
>>> With your permission, I would like to use the Petsc.jl file as the basis
>>> for developing a package.  My plan is create a lower level interface that
>>> exactly wraps Petsc functions, and then construct a higher level interface,
>>> probably an object that is a subtype of Julia's AbstractArray, that allows
>>> users to store values into Petsc vectors and matrices.  I am less
>>> interested in integrating tightly with Julia's existing linear algebra
>>> capabilities than ensuring good scalability.  The purpose of the high level
>>> interface it simple to populate the vector or matrix.
>>>      What do you think, both about using the Petsc.jl file and the
>>> overall approach?
>>>      Jared Crean
>  --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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