Anders Logg wrote: > On Tue, Dec 01, 2009 at 07:58:12PM +0000, Garth N. Wells wrote: >> >> Anders Logg wrote: >>> On Tue, Dec 01, 2009 at 07:21:00PM +0000, 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. >>> I'm warming up to the Array class option in which case we don't need >>> to spend more time on fixing typemaps which will be removed anyway. >>> >>> So should the plan then be to use Array as much as possible in the >>> C++ interface, instead of std::vector? We will still use std::vector >>> and other STL types in the implementation but less of it in the user >>> interface. >>> >> Perhaps, as long as we don't end up re-implementing all the std::vector >> functionality in Array. >> >> Garth > > I assume we will make it fixed-size which will simplify the > implementation a great deal and differentiate it from std::vector > which has push_back. >
Fixed on the C++ side. It should have a function to indicate a change in size. That way, we can have this process 1. An Array is received and turned into a NumPy 2. Length of NumPy array changes on the Python side 3. Array is 'informed' of the new length when sent back to C++ This change in length on the Python side is something we can't handle at the moment as far as I understand. Garth > ok, so let's wait for you to revert the changes to eval() and then see > where we stand. > > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
