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Comment by montebicyclelo

Incorrect Pytorch gradients with Apple MPS backend...

Yep this kind of thing can happen. I found and reported incorrect gradients for Apple's Metal-backed tensorflow conv2d in 2021 [1].

(Pretty sure I've seen incorrect gradients with another Pytorch backend, but that was a few years ago and I don't seem to have raised an issue to refer to... )

One might think this class of errors would be caught by a test suite. Autodiff can be tested quite comprehensively against numerical differentiation [2]. (Although this example is from a much simpler lib than Pytorch, so I could be missing something.)

[1] https://github.com/apple/tensorflow_macos/issues/230

[2] https://github.com/sradc/SmallPebble/blob/2cd915c4ba72bf2d92...

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