also update the ragged_all_to_all docstring. pseudocode in the style of the shard_map tutorial would be better and cleaner, but it needs the context of the tutorial to explain; i'll add ra2a to the shmap tutorial in the future.
PiperOrigin-RevId: 735957604
In a singleton group case, unlike regular all_to_all, the ragged op becomes a generic equivalent of DynamicUpdateSlice, except update size is not statically known. This operation can't be expressed with standard HLO instructions -- the backend will handle this case separately.
Added small improvement to error messages.
PiperOrigin-RevId: 721473063
