[Numpy-discussion] failed to add routine to the core module

[marc]

Hello Marten,

Thank you for your help, effectively, the example that you propose is 
much easier to imitate, I can now continue further.

Thanks,
Marc

On 05/18/2017 04:32 PM, Marten van Kerkwijk wrote:
> Hi Marc,
>
> ufuncs are quite tricky to compile. Part of your problem is that, I
> think, you started a bit too high up: `divmod` is also a binary
> operation, so that part you do not need at all. It may be an idea to
> start instead with a PR that implemented a new ufunc, e.g.,
> https://github.com/numpy/numpy/pull/8795, so that you can see what is
> involved.
>
> All the best,
>
> Marten
>
>
>
> On Thu, May 18, 2017 at 9:04 AM, marc <marc.barbry at mailoo.org> wrote:
>> Dear Numpy developers,
>>
>> I'm trying to add a routine to calculate the sum of a product of two arrays
>> (a dot product). But that would not increase the memory (from what I saw
>> np.dot is increasing the memory while it should not be necessary). The idea
>> is to avoid the use of the temporary array in the calculation of the
>> variance ( numpy/numpy/core/_methods.py line 112).
>>
>> The routine that I want to implement look like this in python,
>>
>> arr = np.random.rand(100000)
>> mean = arr.mean()
>> var = 0.0
>> for ai in arr: var += (ai-mean)**2
>>
>> I would like to implement it in the umath module. As a first step, I tried
>> to reproduce the divmod function of umath, but I did not manage to do it,
>> you can find my fork here (the branch with the changes is call
>> looking_around). During compilation I get the following error,
>>
>> gcc: numpy/core/src/multiarray/number.c
>> In file included from numpy/core/src/multiarray/number.c:17:0:
>> numpy/core/src/multiarray/number.c: In function ‘array_sum_multiply’:
>> numpy/core/src/private/binop_override.h:176:39: error: ‘PyNumberMethods {aka
>> struct <anonymous>}’ has no member named ‘nb_sum_multiply’
>> (void*)(Py_TYPE(m2)->tp_as_number->SLOT_NAME) != (void*)(test_func))
>>                              ^
>> numpy/core/src/private/binop_override.h:180:13: note: in expansion of macro
>> ‘BINOP_IS_FORWARD’ if (BINOP_IS_FORWARD(m1, m2, slot_expr, test_func) && \
>>          ^
>> numpy/core/src/multiarray/number.c:363:5: note: in expansion of macro
>> ‘BINOP_GIVE_UP_IF_NEEDED’ BINOP_GIVE_UP_IF_NEEDED(m1, m2, nb_sum_multiply,
>> array_sum_multiply);
>>
>> Sorry if my question seems basic, but I'm new in Numpy development.
>> Any help?
>>
>> Thank you in advance,
>>
>> Marc Barbry
>>
>> PS: I opened an issues as well on the github repository
>> https://github.com/numpy/numpy/issues/9130
>>
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