Fix local Fourier transforms (conjugated) over non-binary fields - #579
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…njugate QuditCode.conjugated() transformed the chosen qudits with a plain X<->Z swap, which is symplectic only over GF(2). Over odd characteristic the missing sign negates each conjugated qudit's contribution to every symplectic product, so commutation relations were corrupted: the conjugated code was inconsistent (BaconShorCode(3, field=3).conjugated([0, 5, 7]) reported dimension 3 instead of 1) and its logical operators were not a valid basis. Apply the local Fourier map (x, z) -> (z, -x) via math.symplectic_conjugate, restricted to the chosen qudits, so the conjugation convention has a single source of truth. Over GF(2) this is unchanged, since -1 == 1. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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AI-assisted summary
QuditCode.conjugated()previously transformed the chosen qudits by swapping their X-type and Z-type components. That swap is symplectic only over GF(2); over a field of odd characteristic it drops a sign and flips the commutation relations of the conjugated qudits.QuditCode.conjugated()now applies the local Fourier map (x, z) -> (z, -x) throughmath.symplectic_conjugate, restricted to the chosen qudits, so the conjugation convention lives in one place.A regression test checks that conjugating a code over GF(3) and GF(4) preserves its commutation relations, dimension, and logical operator basis.