[petsc-users] petsc4py and numpy

[Matthew Knepley]

On Tue, May 8, 2012 at 3:11 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:

> On 8 May 2012 12:25, Matthew Knepley <knepley at gmail.com> wrote:
> > On Tue, May 8, 2012 at 11:15 AM, Lisandro Dalcin <dalcinl at gmail.com>
> wrote:
> >>
> >> On 8 May 2012 12:04, Matthew Knepley <knepley at gmail.com> wrote:
> >> > On Tue, May 8, 2012 at 11:00 AM, Christian Staudt
> >> > <christian.staudt at ira.uka.de> wrote:
> >> >>
> >> >> Matthew Knepley <knepley at gmail.com> wrote:
> >> >>
> >> >> a) Is there an easy and efficient way to convert a numpy.ndarray to a
> >> >>
> >> >> PETSc.Vec or PETSc.Mat (and vice-versa)?  (A PETSc.Vec.getArray()
> >> >> returns
> >> >> a
> >> >>
> >> >> numpy.ndarray, though I have found no such method for PETSc.Mat yet.
> )
> >> >>
> >> >>
> >> >>
> >> >> If you are using dense matrices (MATDENSE) then MatGetArray() works.
> >> >>
> >> >>
> >> >> I don't think this is implemented in petsc4py: At least, there's no
> >> >> method
> >> >> PETSc.Mat.getArray()
> >> >
> >> >
> >> > If you ask Lisandro for it, he will put it in.
> >> >
> >>
> >> Matt, I've never put that in just because I'm not sure how to make it
> >> general. PETSc have many different matrix formats, and MatGetArray()
> >> call is like a hack, where you can get very different things (the "1D"
> >> values of an AIJ matrix, the "2D" values of a dense matrix in Fortran
> >> order). What about MPIAIJ, what should I return to users? Can you
> >> suggest some approach or API to implement this (I mean, how to get
> >> arrays for the various matrix types)?
> >
> >
> > I think the whole point is that you should not do it. However, that has
> > never stopped us from giving users
> > what they ask for. We are not int he business of reforming computing
> > practices, which is why we have
> > MatGetArray(). I would make a wrapper that failed unless the type was
> > MATDENSE.
> >
>
> Yea, that's really easy.
>
> However, Is there anything better for AIJ matrices? Right now, we have
> mat.getValuesCSR()... it works by calling MatGetRow() row by row twice
> (first pass to count and allocate, next to get values and copy to
> NumPy arrays).


For AIJ specifically, you can use MatGetIJ() and MatGetArray().

   Matt


>
> --
> Lisandro Dalcin
> ---------------
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experiments is infinitely more interesting than any results to which their
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