On Tuesday 01 December 2009 11:51:20 Anders Logg wrote: > On Tue, Dec 01, 2009 at 07:16:36PM +0000, Garth N. Wells wrote: > > Anders Logg wrote: > > > On Tue, Dec 01, 2009 at 07:06:43PM +0000, Garth N. Wells 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. > > > > > > I thought we should not name it Array so as to not encourage use of > > > it, or do you suggest using it instead of std::vector. > > > > Yes. > > > > > I was thinking of having it in addition to std::vector. > > > > We would have multiple versions of eval functions if we support > > std::vector and Array. It wouldn't be clear to a user which to use. > > Also, we could avoid some copying of data if we use Array since an Array > > could be initialised with a pointer to some data, whereas a vector can't. > > It makes sense, but I'll need some more convincing. We have an Array > class before. The reason I added it then was that we wanted a > nice-looking interface with minimal visibility of other libraries. > We also had a List class for a linked list etc. > > But having an Array class does make some sense considering we have > Vector and Matrix classes (that happen to be implemented using for > example PETSc).
Having an Array class do make sense as DOLFIN is a two language library. > > >>> 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 good. > > > > > >>> 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. > > > > > > Good point, but if it's possible to fix with moderate work I suggest > > > we (Johan...) fix it before the release. > > > > > > This might be the last release in a long time with major interface > > > changes to the Expression/Function classes and then it would be good > > > to have it all in place at once. > > > > You mean that you want a new Array class in place? I don't think that is > > feasible in a short time. > > > > Garth > > No, not if we go for that option. Then it doesn't really matter about > the real* vs std::vector thing. > > But the Python interface will remain unchanged which is good. C++ > users are a bit more hardcore and can live with the changes. ??? Johan _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
