handle complex phases in .to_adjoint and .conjugate

[dlyongemallo]

Fixes #380.

[Copilot]

Pull request overview

This PR fixes issue #380 by implementing proper handling of complex phases in the .to_adjoint() and .conjugate() methods across the PyZX codebase. Previously, these methods simply negated phases, which is incorrect for complex-valued phases that can arise in symbolic computations.

Changes:

• Added Poly.conjugate() method to properly conjugate complex coefficients in polynomials
• Updated Scalar.copy() to handle complex phases using (-phase).conjugate() transformation
• Modified Gate.to_adjoint() to apply the same transformation for complex Poly phases
• Added comprehensive test coverage for all three components

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pyzx/symbolic.py	Adds conjugate() method to Poly class that conjugates complex coefficients while preserving real coefficients
pyzx/graph/scalar.py	Updates copy() method with helper function to properly conjugate complex phases in all scalar fields
pyzx/circuit/gates.py	Modifies to_adjoint() to detect Poly phases and apply (-phase).conjugate() transformation
tests/test_symbolic_parsing.py	Adds test class with coverage for real, complex, and pure imaginary polynomial coefficients
tests/test_scalar.py	Adds tests for scalar conjugation with complex phases in phase, phasenodes, and sum_of_phases
tests/test_circuit.py	Adds tests for gate adjoint operations with real, symbolic, and complex phases

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[jvdwetering]

Does this make sense? It looks like you are conjugating twice

[dlyongemallo]

I don't understand. To compute the adjoint of e^{i π phase}, we need e^{-i π phase*} where phase* is the complex conjugate of phase. So (-phase).conjugate() is the correct value, isn't it?

Is the brackets that's the problem? Since negation and conjugation commute, I can remove them.

[jvdwetering]

Same here, it looks like you are conjugating twice

[jvdwetering]

I'm a little bit confused about certain lines where it looks like you are conjugating the value twice. Could you take a look?

[dlyongemallo]

I think I encountered a bug while trying to write a test for this. In these lines from symbolic.py, terms with complex coefficients are filtered out when doing the mod operation.

In set_phase it does a phase % 2 here, terms with complex coefficients are all dropped. Surely this is wrong?

[dlyongemallo]

Ah, that was noticed in #377 already, but for multigraph.py.