Hello,
I agree with Matt, all the functions PetscOptions*(...) pass
standard C data types, so Julia can call them directly. For well
written interfaces like Petsc's, I prefer very thin wrappers that
provide as similar a user experience as possible to the original
interface. For the higher level interface, my goal is to provide
abstraction for populating the array but not for creating it or doing
math with it, so there is no violation of the abstraction by allowing
option setting.
As for typing, I think the wrappers should employ the same
abstract that Petsc itself does and typealias PetscInt, PetscScalar etc.
to the proper Julia types, and use those aliases for all the wrapper
functions.
To find out the proper sizes, PetscInitialize can be called with
no arguments, and then PetscDataTypeGetSize(PETSC_TYPE,&sz) can be
used to figure out the required type.
Patrick, by bitbucket username is jcrean. I'd definitely like
to take a look at your slides. I did some reading about Julia on
PowerPC, and the results aren't good. I think running on the BG will
have to wait for statically compiled Julia. For now, I am targeting an
1024 core Sandy Bridge cluster with InfiniBand.
Jared Crean
On 7/6/2015 9:02 AM, Matthew Knepley wrote:
On Mon, Jul 6, 2015 at 4:59 AM, Patrick Sanan <[email protected]
<mailto:[email protected]>> 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 <[email protected]
<mailto:[email protected]>> 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
