On 6 July 2015 at 14:56, Matthew Knepley <[email protected]> wrote: > On Mon, Jul 6, 2015 at 8:40 AM, Patrick Sanan <[email protected]> > wrote: >> >> On Mon, Jul 6, 2015 at 3:02 PM, Matthew Knepley <[email protected]> wrote: >>> >>> On Mon, Jul 6, 2015 at 4:59 AM, Patrick Sanan <[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? >> >> I don't see any fundamental problems with this, either, but in practice >> people tend to want to hardcode things (like the deal.ii interface does, in >> my limited experience with it). Hopefully this is just a suboptimal design >> choice which can be avoided with an interface to the options database >> included in the wrapper. > > > The deal.II wrapper is crazy. I have told Wolfgang. It makes the same > mistake as FEniCS, which is to provide > an interface type for each PETSc implementation type. This kind of confusion > takes a flexible, runtime configuration > and makes it an inflexible, compile-time configuration while introducing a > load of new types and making the > closed-world assumption. >
Your assertion on the FEniCS interface to PETSc is wrong for recent FEniCS; users can set PETSc object types via the PETSc options system, and users can access and manipulate directly the PETSc object, if they wish (or initialise a wrapper with a PETSc object). Garth >>> On the other hand, requiring specific types, ala FEniCS, >>> is very limiting. >> >> What tradeoffs does FEniCS make in this context? Are there other wrappers >> which make different ones? >> How wrong is it to say "If we have real and complex double types, 99% of >> the use cases are covered?". > > > I think this is essentially true, and is what is done by the Purdue guys. > You can accomplish it by using dynamic > libraries and a fair bit of hacking. C still does not have a great way to do > this, but I am hopeful for the Karl-style > type handling from GPUs migrated to handle the real/complex divide. > > Matt > >> >> >>> >>> >>> Matt >>> >>>> >>>> On Sat, Jul 4, 2015 at 11:00 PM, Jared Crean <[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 >> >> > > > > -- > 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
