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

[Marten van Kerkwijk]

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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