gradient question about GatherScatterMode

[Dong-Jiahuan]

Hello, In https://jax.readthedocs.io/en/latest/jax.lax.html#jax.lax.GatherScatterMode, it says Gradients will not be correct if indices are out-of-bounds. (in PROMISE_IN_BOUNDS mode)

(1) I want to know If gradients will be correct or not when indices are out-of-bounds in modes other than PROMISE_IN_BOUNDS ?
(2) For example, the document says out-of-bounds gathers will be clamped. Does it mean when you use lax.gather and indices are out-of-bounds and choose PROMISE_IN_BOUNDS mode, it's totally equivalent to choose CLIP mode ? (the results are same, gradients are both incorrect in both modes...)

These two questions above are the same question to some degree...

[hawkinsp]

1. Only PROMISE_IN_BOUNDS mode has incorrect gradients. The other modes will have correct gradients.
2. Exactly what PROMISE_IN_BOUNDS does is up to the implementation, but it's is equivalent to CLIP in the forwards direction, while its gradient is equivalent to DROP. (These don't match, which is why the result isn't correct.)

[Dong-Jiahuan]

I see. Thanks!