Johan Hake wrote: > On Tuesday 01 December 2009 12:08:54 Garth N. Wells wrote: >> 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. > > A NumPy array is already fixed. Any changes wrt length will return a new > NumPy > array. You can hand slices, which are views of other arrays, but this is > different case which we cannot support. > > If we have a re-sizable Array we can add some flags, so it cannot be resized > if it is a view of a passed NumPy array. >
When will a NumPy array destroy its data? > But shouldn't this discussion be on the Blueprint page? > Yes. Garth > Johan >> 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 >> _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
