[petsc-dev] Julia Petsc Wrapper

Jared Crean jcrean01 at gmail.com
Tue Jul 14 10:56:19 CDT 2015

     Hello everyone,
         I got the package in a reasonably working state and Travis 
testing setup, so I am putting the package up on Github.


         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?

         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.

     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 
> <mailto: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
>     <mailto: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

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