add np.stack

[sangyx]

I have added the diff function of np.stack.

When we extend the code to higher-order derivatives, the situation becomes a bit more complicated. There are some places to improve:

• In some derivative functions, the program may enter an infinite loop. For example, np.sum is used when registering the gradient of np.sum. I plan to add depth attributes to DiffArray or to() to control the order of gradients.
• The function registered in nograd_functions will register the gradient when it is called in the form of ufunc.__call__.
• Consider a cleaner way to control whether the calculation should derive.

Do you have any idea about the above questions?

[hameerabbasi]

Ah, yes. I remember running into this when I was initially working with udiff. Basically, in your approach, it would work as follows:

• The DiffArray.to method should only compute the diff with respect to what's passed in, not anything else.
• DiffArray.backward should only compute the calculation graph, but only for "the current level". The next level should remain "unevaluated" or in the form of a graph until you actually call DiffArray.diff[some_name].backward.

[sangyx]

I have fixed the problem, we have to put all the calculations that need to register gradients in each diff function in lambda g (or vjp), so as to avoid infinite loops.

The error of <uarray multimethod '__instancecheck__'> in ci seem to be related to uarray.

[hameerabbasi]

I'll fix those up. Don't worry about them for now.

[hameerabbasi]

@peterbell10 I can reproduce the segfault in CI. Is it possible for you to investigate? I was also getting a bunch of "returned NULL without setting an error" on determine_backend.

[hameerabbasi]

@sangyx Passing the torch back to you. 😄 The segfaults should be resolved now.

Edit: To resolve them locally, get master of uarray and unumpy, and do pip install -e . in the directories of both.

[sangyx]

Thanks!

[sangyx]

@hameerabbasi Hi, I want to add <uarray multimethod '__instancecheck__'> to raw_functions. But I don't know how to refer it. How can I find it by code like np.ndim?

[hameerabbasi]

Hi, I want to add <uarray multimethod '__instancecheck__'> to raw_functions. But I don't know how to refer it. How can I find it by code like np.ndim?

You can probably do something like unumpy.ClassOverrideMeta.__instancecheck__.

[sangyx]

@hameerabbasi Could you help me to check whether the NoGradBackend is correct?

[hameerabbasi]

Thanks @sangyx!