Conjugate the first argument in vecdot

[asmeurer]

Note that PyTorch uses its own vecdot directly for complex inputs,, which already does conjugation.

This is currently untested by the test suite (data-apis/array-api-tests#312)

Fixes #200.

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array_api_compat/common/_aliases.py:482

• The new behavior of conjugating the first argument in vecdot should be covered by tests.

res = xp.conj(x1_[..., None, :]) @ x2_[..., None]

[ev-br]

The spec stance on rejecting real arguments to complex functions is a bit bizzare. I realize it's probably because xp.imag(real_array) would otherwise have to allocate an array of zeros but still.

[asmeurer]

FWIW, I agree with you that real arguments really should be accepted in conj. We agreed to fix this in a consortium meeting, but it hasn't been updated in the standard yet (and even then, then strict would only use the updated behavior when the version flag is set to 2024). See data-apis/array-api#824 (comment)

At any rate, this isn't a problem here. The reason is that the code in array_api_compat/common/_aliases.py only applies to the libraries numpy, cupy, and dask (and in a small number of cases, torch), all of which allow conj on real inputs.

This is something to be aware of generally. In a lot of the wrappers, we use specific implementation details either of torch or of numpy/cupy/dask when using xp, which are often not things allowed by the array API. It does mean that if we ever want to reuse the same wrapper for another library, we'd have to carefully check that it still works. But the wrappers themselves do not need to follow the array API (otherwise it would be circular, and we wouldn't get anywhere).

resolved

[asmeurer]

And also you don't really ever have to worry about array-api-strict in array-api-compat. The only place it's ever used is it can be returned from array_namespace.

[asmeurer]

I'm going to merge this now, but I'm hopeful we can get testing for this in array-api-tests before we do a release.