Add expectation and trace to tableau python bindings#176
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Pull request overview
Exposes the Rust GeneralizedTableau Pauli expectation (⟨ψ|P|ψ⟩) and summed-pattern trace (Σ⟨ψ|P|ψ⟩) APIs through the Python bindings, and adds Python tests to validate basic correctness on small states (|0⟩, |+⟩, Bell, and a single-qubit ry rotation).
Changes:
- Added
GeneralizedTableau.expectation(word: str) -> floatandGeneralizedTableau.trace(pattern: str) -> floatto the Python wrapper. - Extended the native PyO3 interface to call
inner.expectation(...)/inner.trace(...). - Added pytest coverage for expectation/trace on representative states and patterns.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
ppvm-python/test/generalized_tableau/test_expectation.py |
Adds Python tests for expectation and trace on |
ppvm-python/src/ppvm/generalized_tableau.py |
Adds Python-level convenience methods + docstrings for expectation and trace. |
ppvm-python/src/ppvm/_core.pyi |
Updates native-module type stubs to include expectation and trace. |
crates/ppvm-python-native/src/interface_tableau.rs |
Adds PyO3 methods to expose expectation/trace from the Rust tableau. |
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|
The GeneralizedTableau.expectation docstring advertised "X0Y1" (which panics on the digit) and claimed underscores are ignored (they are dropped from bit placement but still inflate nqubits). Document the actual accepted syntax: a dense I/X/Y/Z string whose length equals the qubit count. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Roger-luo
approved these changes
Jul 13, 2026
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| /// `⟨ψ|word|ψ⟩` for the multi-qubit Pauli string `word`. | ||
| pub fn expectation(&self, word: String) -> f64 { | ||
| let w: PauliWord<<$type as Config>::Storage> = word.into(); | ||
| self.inner.expectation(&w) | ||
| } |
Comment on lines
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| /// `Σ_{P matches pattern} ⟨ψ|P|ψ⟩`. | ||
| pub fn trace(&self, pattern: String) -> f64 { | ||
| let pat: PauliPattern = pattern.into(); | ||
| self.inner.trace(&pat) | ||
| } |
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This wasn't added as part of #172, but should be exposed in python too.