[Numpy-discussion] Numpy FFT normalization options issue (addition of new option)

[Ross Barnowski]

I think it's also important to get the thoughts of the SciPy community on
this topic so that we avoid divergence between numpy.fft and scipy.fft. I
would recommend sending this discussion to the scipy mailing list as well.

~Ross

On Tue, Jun 23, 2020 at 4:11 PM Feng Yu <rainwoodman at gmail.com> wrote:

> Your approach sounds good to me.
>
> Thanks,
>
> Yu
>
> On Tue, Jun 23, 2020 at 11:51 AM Chris Vavaliaris <cv1038 at wildcats.unh.edu>
> wrote:
>
>> Chris Vavaliaris wrote
>> > Hello,
>> >
>> > - my first reaction would be that the less argument names we change at a
>> > time the better, so that we don't confuse people or cause codes written
>> > with
>> > previous NumPy versions to break. Personally I always think of "ortho"
>> as
>> > "orthonormal", which immediately brings "unit norm" to mind, but I have
>> no
>> > problem whatsoever with changing its name to "unitary" or maybe "unit",
>> > which I'd probably choose if we were writing the routines from scratch.
>> >
>> > - In terms of the "inverse" name option, I do believe that it'd be a
>> > confusing choice since "inverse" is used to describe the inverse FFT; if
>> > we
>> > choose to stick with a name that's based on the fact that this scaling
>> is
>> > opposite to the "norm=None" option, then I'd suggest "norm=opposite" as
>> a
>> > better choice. However, following Ross' comment, I think we could
>> choose a
>> > name based on the fact that the forward transform is now scaled by `n`,
>> > instead of the backward one as in the default "norm=None". In this case,
>> > I'd
>> > suggest "norm=forward", which we can also nicely abbreviate to the
>> > 4-character form "norm=forw" if desirable.
>> >
>> > Chris
>> >
>> >
>> > Feng Yu wrote
>> >> Hi,
>> >>
>> >> 1. The wikipedia pages of CFT and DFT refer to norm='ortho' as
>> 'unitary'.
>> >> Since we are in general working with complex numbers, I do suggest
>> >> unitary
>> >> over ortho.
>> >> (https://en.wikipedia.org/wiki/Fourier_transform#Other_conventions)
>> and (
>> >>
>> https://en.wikipedia.org/wiki/Discrete_Fourier_transform#The_unitary_DFT)
>> >>
>> >> 2. I share Chris's concern about 'inverse', but I could not come up
>> with
>> >> a
>> >> nice name.
>> >>
>> >> 3. Now that we are at this, should we also describe the corresponding
>> >> continuum limit of FFT and iFFT in the documentation?
>> >>
>> >> A paragraph doing so could potentially also help people diagnose some
>> of
>> >> the normalization factor errors. I assumed it is common that one needs
>> to
>> >> translate a CFT into DFT when coding a paper up, and the correct
>> >> compensation to the normalization factors will surface if one does the
>> >> math. -- I had the impression 1 / N corresponds to 1 / 2pi if the
>> >> variable
>> >> is angular frequency, but it's been a while since I did that last time.
>> >>
>> >> - Yu
>> >>
>> >> NumPy-Discussion mailing list
>> >
>> >> NumPy-Discussion@
>> >
>> >> https://mail.python.org/mailman/listinfo/numpy-discussion
>> >
>> >
>> >
>> >
>> >
>> > --
>> > Sent from: http://numpy-discussion.10968.n7.nabble.com/
>> > _______________________________________________
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>>
>> > NumPy-Discussion@
>>
>> > https://mail.python.org/mailman/listinfo/numpy-discussion
>>
>> Hello all,
>> the discussion on this topic has been stagnant for the past couple of
>> weeks,
>> so I just wanted to ask if anyone has any alternative names for the new
>> normalization option that would like to share.
>>
>> If not, I'd suggest that we move on with "norm=forward", which seems to
>> be a
>> more straightforward choice than the "norm=inverse" naming alternative. I
>> can wait a couple of days for possible new recommendations to be
>> submitted,
>> and will then recommit to the open PR to account for the new kwarg name.
>>
>> In terms of the name for the "norm=ortho" option, I suggest that we keep
>> it
>> as is for now so that we don't introduce two API changes at once. If
>> desired, we can discuss it separately and open a new PR introducing a name
>> such as "norm=unitary" or "unit" as recommended in previous messages. I'm
>> happy to handle that if you think it'd be a useful change.
>>
>> Chris
>>
>>
>>
>>
>>
>> --
>> Sent from: http://numpy-discussion.10968.n7.nabble.com/
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