Fix _call not implemented error in call_and_ladj

[felixdivo]

Some transformations do not implement _call, even some of the Pytorch ones like ComposeTranform.

https://github.com/pytorch/pytorch/blob/4869929f32c176dc3e5ea4cd4164b3fd73a0c9ea/torch/distributions/transforms.py#L270-L385

This results in call_and_ladj raising a NotImplementedError.

>>> import zuko
>>> t = zuko.transforms.ComposeTransform([])
>>> t.call_and_ladj(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../zuko/transforms.py", line 41, in _call_and_ladj
    y = self._call(x)
  File ".../torch/distributions/transforms.py", line 176, in _call
    raise NotImplementedError
NotImplementedError

[felixdivo]

Curiously, the test fails if I add ComposeTransform([IdentityTransform(), SinTransform()]). I think this is unrealted, but I think should be investigated?

[francois-rozet]

Hello @felixdivo,

Thanks for reporting the bug and finding a solution. Could you address my comments before I merge?

the test fails if I add ComposeTransform([IdentityTransform(), SinTransform()])

This is because SinTranform is bijective between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$. In ComposeTransform, the domain constraint is invisible for the test. So it defaults to $[-5, 5]$.

As a side note, per the contribution guidelines:

If you found a bug and want to fix it, please create an issue reporting the bug before creating a pull request. Similarly, if you want to add a new feature, first create a feature request issue. This allows to separate the discussions related to the bug/feature, from the discussions related to the fix/implementation.

[felixdivo]

As a side note, per the contribution guidelines

Thanks for the hint and sorry for not reading it. I'll follow it from now on. I wasn't aware of it.