dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Nov 18, 2009 at 05:23:47PM +0100, Johan Hake wrote:
> On Monday 16 November 2009 22:03:13 DOLFIN wrote:
> > One or more new changesets pushed to the primary dolfin repository.
> > A short summary of the last three changesets is included below.
> >
> > changeset:   7459:739b7539d6eb
> > tag:         tip
> > user:        "Garth N. Wells <gnw20@xxxxxxxxx>"
> > date:        Mon Nov 16 21:02:54 2009 +0000
> > files:       dolfin/swig/numpy_typemaps.i dolfin/swig/std_vector_typemaps.i
> >  site-packages/dolfin/expression.py description:
> > Get typemap(in) for std::vector working.
> >
> > Seems to work but I don't know if it's any good.
>
> (Resending the email as I forgot to send it using the correct email adress...)
>
> I haven't got the time to look at it, but yes the provided typemaps do make a
> copy, which is not optimal. I have have actually been a bit worried ;) that
> you might change the interface of eval, and possible other methods too, from
> double* to std::vector. In most perspectives it is much nicer to pass a
> std::vector, not least for safety. However std::vector is more difficult to
> interact with NumPy.
>
> SWIG do provide it's own implementation of std::vector which more or less wrap
> the c++ interface of a vector seamless. We have used this to pass arguments of
> std:vector previously. However the amount of code that is produced and not
> used is large (~1MB for DOLFIN version < 9.2). NumPy arrays and lists are also
> much more convenient structures to work with in Python.
>
> I have therefore decided to remove the dependency of std_vector.i by adding
> our own typemaps for std::vector arguments. Each one of those typemaps do make
> a copy. For now we have typmaps for primitives and pointers so each copy
> should not be that bad. But for operations that is performed alot of times, it
> might be a difference. But I doubt it would for the callback functionality, as
> I assume just calling the python function would take most of the time.
>
> We could consider creating a NumPy array from the pointer to the first element
> of the vector, as I have seen you have discussed on the list previously, for
> other cases. We then have to consider the life time of the vector. For
> director typemaps that would probably be ok. For other "out" typemaps it might
> not be ok.
>
> Would it be an option to add, in C++, a small template wrapper class for
> arrays that are supposed to go back and forth to Python via NumPy arrays?
> Including basic operations so it will be useful also in C++.

We have had such a class before named simple_array but it was removed
at some point.

--
Anders


> Johan
>
> >
> > changeset:   7458:f9d6aeab7271
> > user:        "Garth N. Wells <gnw20@xxxxxxxxx>"
> > date:        Mon Nov 16 19:06:12 2009 +0000
> > files:       demo/function/eval/python/demo.py
> >  site-packages/dolfin/expression.py description:
> > Comment out some dim checks in expression.py.
> >
> >
> > changeset:   7457:6dc505f97225
> > user:        "Garth N. Wells <gnw20@xxxxxxxxx>"
> > date:        Mon Nov 16 15:13:08 2009 +0000
> > files:       demo/function/eval/python/demo.py dolfin/swig/docstrings.i
> >  dolfin/swig/function_post.i dolfin/swig/function_pre.i
> >  dolfin/swig/std_vector_typemaps.i description:
> > Add empty typemap for NumPy array to std::vector<double>.
> >
> > ----------------------------------------------------------------------
> > For more details, visit http://www.fenics.org/hg/dolfin
> > _______________________________________________
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> > DOLFIN-dev@xxxxxxxxxx
> > http://www.fenics.org/mailman/listinfo/dolfin-dev
> >
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