Rewrite 1/x**(-a) -> 1 * x**a#2199
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Jun 8, 2026
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- Centralize cached constant predicates in constant_props module
- Rewrite division by a reciprocal or negative power as multiplication
Move the tag-cached, constant-data predicates into a new dependency-free leaf module `pytensor.tensor.constant_props`: - `constant_indices_are_unique` and `constant_is_arange` (from `rewriting/subtensor.py`) - `constant_is_all_negative` (new; replaces the inline all-negative scan in `local_sign_div`) These only inspect constant data, so the module imports nothing beyond numpy and `Constant`. The recursive, graph-walking sign analysis `is_provably_positive` / `is_provably_non_negative` stays in `subtensor` with the ops it recurses over, and is renamed to drop the leading underscore now that it is imported across modules.
Add two specialize rewrites: - `local_div_reciprocal_to_mul`: `A / reciprocal(B) -> A * B` and `A / y ** (-p) -> A * y ** p`. The first form is left opaque by the AlgebraicCanonizer and is what `local_pow_specialize` emits for negative constant exponents (e.g. `y ** -2 -> reciprocal(sqr(y))`), which previously left a redundant reciprocal and division. - `local_reciprocal_neg_pow_to_pow`: `reciprocal(y ** (-p)) -> y ** p`, covering `1 / y ** (-p)`, which `local_div_to_reciprocal` canonicalizes to a reciprocal before it can reach the division rewrite. Both only fire when the exponent is recognisably negative (a `neg` node or an all-negative constant), so a positive exponent is never flipped.
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