Dft reverse axis

[lanougue]

Handle decreasing coordinates in dft with true_phase = True.
Add a test to check

[lanougue]

@roxyboy, merge ?

[roxyboy]

I'm personally ok to merge but I think we should wait for @rabernat 's approval as well. He should be back from vacation next week.
We should also probably update the docs page using realistic data from the xarray tutorial (e.g. #144 ).

[rabernat]

Thanks so much for this PR @lanougue! I really appreciate your work.

I agree with @roxyboy that documentation of this behavior is needed in the public facing docstrings and / or narrative documentation.

[rabernat]

I don't understand this comment, specifically (CAUTION : [] diff None).

[lanougue]

Sorry for this not being explicit. This is to emphasize that:
np.flip(a, axis=None) has a different behaviour than np.flip(a, axis=[]).
If axis=None, all axis are flipped.
If axis=[], no axis are flipped
I though it deserved to me mentioned in a comment

[rabernat]

For the sake of the other devs, I would prefer to make this all a bit more explicit, i.e.

if coord[-1] > coord[0]:
    coord_data = coord.data
else:
    coord_data = np.flip(coord.data, axis=-1)
lag = coord_data / (len(coord.data) // 2)

[lanougue]

ok but the last line should then be:
lag = coord_data[(len(coord.data)) // 2]

[rabernat]

Thanks! So is the plan to defer the documentation updates to a future PR? If so, I will merge.

[roxyboy]

Thanks! So is the plan to defer the documentation updates to a future PR? If so, I will merge.

I give a thumbs up to a separate PR for docs :)