dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Tuesday 01 December 2009 11:21:00 Garth N. Wells wrote:
> Johan Hake wrote:
> > On Tuesday 01 December 2009 11:06:43 you wrote:
> >> Anders Logg wrote:
> >>> On Tue, Dec 01, 2009 at 09:59:18AM -0800, Johan Hake wrote:
> >>>> On Tuesday 01 December 2009 00:45:50 Anders Logg wrote:
> >>>>> Would it help to add a new class on the C++ side that is used only
> >>>>> for passing array data back and forth between C++ and Python? We have
> >>>>> had this before (SimpleArray) and it would be fairly easy to extend
> >>>>> the C++ with extra functions in the interface that use SimpleArray
> >>>>> instead of std::vector.
> >>>>>
> >>>>> Then perhaps we can have one single typemap that hits SimpleArray
> >>>>> everywhere and converts it to a NumPy array.
> >>>>
> >>>> Yes, something in that direction is what I had in mind. In addition we
> >>>> could also add a foo.array() function to get a NumPy view from this
> >>>> class. This would be nice when we do not want to have all the
> >>>> communication through typemaps, but actually using the SimpleArray in
> >>>> Python as return argument from some function that wants to resize the
> >>>> array.
> >>>>
> >>>> We would also need some stuff to handle memory management.
> >>>>
> >>>> I see two fundamental ways such a class could be used:
> >>>>   1) A replacement for the previous use of double/uint/int*, now
> >>>> std::vector 2) A replacement for communication using std::vector where
> >>>> resize flexibility is needed.
> >>>>
> >>>> I think 1, speaks for it self. 2 is where we need to resize any passed
> >>>> vector. This goes for GenericMatrix.getrow, foo.intersection,
> >>>> GenericFunction.comput_vertex_values.
> >>>>
> >>>>> And the work would be to add the extra stuff on the C++ side. The
> >>>>> advantage would be less complex wrapper code and that Garth and I
> >>>>> are capable of handling the complexities on the C++ side.
> >>>>
> >>>> Yes this must be a goal. I agree that the present SWIG situation has
> >>>> grown out of hands.
> >>>>
> >>>>> But what I don't understand is why it would be easier to write a
> >>>>> typemap for SimpleArray than for std::vector. Both of them use
> >>>>> contiguous memory.
> >>>>
> >>>> Yes, but in std::vector it is now way, I suppose, to prevent a vector
> >>>> to delete its data when it goes out of scope. This is necessary in a
> >>>> typical in typemap.
> >>>
> >>> ok, let's create a very flexible array class that is targeted at
> >>> simple communication between C++ and Python/NumPy. We had a class
> >>> before named SimpleArray. We might call it NumPyArray or PythonArray.
> >>
> >> Can we just call it Array? It will be visible in the C++ interface (e.g.
> >> in eval) so it would be good to have a nice name.
> >
> > Agree.
> >
> >>> I have created a blueprint:
> >>>
> >>> https://blueprints.launchpad.net/dolfin/+spec/array-typemaps
> >>
> >> I'll add something. I was thinking already about this. With a smart
> >> pointer to the underlying data we should be to devise an elegant memory
> >> model and be able to tell an Array object when it does and doesn't own
> >> the data upon construction, and be able to change during execution.
> >
> > Sounds fancy.
> >
> >>> We can fill out the details together.
> >>>
> >>>> I will fix the interface of getrow this evening. I was about to do it
> >>>> yesterday, but instead I got grumpy :) But a good night sleep makes
> >>>> wonders!
> >>>
> >>> Good! :-)
> >>>
> >>> Will you make a fast/temporary fix so that we can get ready for a
> >>> release of 0.9.5 and then we can move the PythonArray implementation
> >>> to a future release?
> >>
> >> The fast fix would be revert back to the
> >>
> >>     eval(double*, std::vector<double>&)
> >>
> >> interface. No point wasting time on typemaps for std::vector if we're
> >> not going to use them.
> >
> > Fell free to make this change, I have a fool proof plan for the other
> > temporary fix though. No new typemaps, just reusing old ones.
> 
> OK, we need to make a decision.
> 
> Option 1: Revert changes to eval.
> 
> Option 2: Get SWIG working with the eval(std::vector<double>&, const
> std::vector<double>&) interface.
> 
> What's it going to be? I'm inclined to Option 1 since it requires no
> work and it's been well tested.

Isn't the amount of files that are touched with option 1 much larger (all 
cpp/demos)? But if you do the changes feel free. I can take a look at it this 
evening if there's something left to do. The new expression.py should at least 
still be working I think, only compile_expressions.py needs an update.

Johan

> Garth
> 
> > Johan
> >
> >> Garth
> >>
> >>> --
> >>> Anders
>