On Tue, Mar 9, 2010 at 9:29 AM, Dag Sverre Seljebotn
<[email protected]> wrote:
> Dag Sverre Seljebotn wrote:
>> Ondrej Certik wrote:
>>
>>> On Tue, Mar 9, 2010 at 12:35 AM, Dag Sverre Seljebotn
>>> <[email protected]> wrote:
>>>
>>>
>>>> Ondrej Certik wrote:
>>>>
>>>>
>>>>> On Thu, Mar 4, 2010 at 4:05 AM, Dag Sverre Seljebotn
>>>>> <[email protected]> wrote:
>>>>>
>>>>>
>>>>>
>>>>>> Are anybody aware of a library for solving ODEs with fast callbacks to
>>>>>> Cython? The ones in SciPy require a Python callback at every step...
>>>>>>
>>>>>> My needs aren't particularily complicated.
>>>>>>
>>>>>> I'll just wrap something in C otherwise, of course (such as GSL).
>>>>>>
>>>>>>
>>>>>>
>>>>> If you do so, please post the code online. I want to see how you did
>>>>> the callbacks (so that it works both in python and cython), as I will
>>>>> need to implement the same things for our solvers. So far I just
>>>>> created a cdef function, that I register for the C callback. But it is
>>>>> not visible from Python.
>>>>>
>>>>>
>>>>>
>>>> I'll have a look at the stuff in Sage first, then try sundials if my
>>>> needs aren't met there...
>>>>
>>>> As for doing the callbacks, I'd do what Sage essentially does:
>>>>
>>>> cdef class DoubleFunction:
>>>> cdef double evaluate(double x):
>>>> raise NotImplementedError()
>>>>
>>>> On the Python frontend side, one can trivially write a coercer object to
>>>> wrap Python callbacks if such are supplied. On the backend side, if you
>>>>
>>>>
>>> I understand this on the backend (C) side, that's clear. But on the
>>> Python side --- how would that be done? E.g. subclassing it? Would
>>> then
>>>
>>> cdef double call_double_func(double x, void* ctx):
>>> return (<DoubleFunction>ctx).evaluate(x)
>>>
>>> evaluate my Python method? Wow, that would be super awesome, never
>>> thought about it (I also wanted to try cpdef instead). Let me try it.
>>>
>>>
>>
>> If you do
>>
>> cdef class DoubleFunction:
>> cpdef double evaluate(...) # NOTE cpdef
>>
>> then yes, you can subclass it in Python. However there's a slight
>> performance penalty for Cython code then (one if-test for NULL-ness of
>> object dict) which might or might not matter.
>>
> Well, in practice it never matters I suppose. The main point is that I
> consider it unfriendly to not allow any callables from Python code, and
Yes, I totally agree.
> the code below satisfies both requirements (fast => DoubleFunction in
> Cython without anything in-between; don't care about speed => use slower
> wrapper and generic callable).
Where is the code in Sage? I did:
sage: search_src("odeint")
sage:
and it didn't find it.
Ondrej
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