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A derivative near zero point two becomes exactly zero in reverse mode. This is an actual MLX CPU result.

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The function is one hundred million times exp minus one, evaluated at minus twenty. Forward mode gives approximately zero point two zero six one one five.

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The backward rule reconstructs the derivative from the rounded output plus one. Once the output rounds to minus one, the derivative disappears.

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Computing exp directly repairs the tested float thirty two cases. But float sixty four also needs the already reported exp correction; otherwise some cases regress.

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The combined change passes all two hundred sixteen native comparisons, including second and third derivatives. Tests and all four control variants are public.

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An analogous JAX report is credited. This is an MLX implementation audit, with no global priority claim. GPU behavior and performance remain untested.