Fix MR-family measurement noise double counting#124
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…t noise - Fixed `MR`, `MRX`, and `MRY` functions to ensure measurement flip probability is not counted as both a pre-measurement Pauli error and a measurement-result flip. - Added unit tests to verify that MR-family instructions correctly handle measurement noise without double-counting. - Updated CHANGELOG to reflect these changes.
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Pull request overview
Fixes an issue in the Stim-to-GraphRepresentation parser/execution path where MR-family demolition measurements with a nonzero flip probability were applying the same flip noise twice.
Changes:
- Remove the redundant pre-measurement
x_errorapplication fromMR,MRX, andMRYinstruction handlers (leaving the single flip-noise application done bym(..., p=...)). - Add unit tests covering probability-bearing instructions and specifically verifying MR-family doesn’t create two independent noise channels for a single probability.
- Document the behavioral fix in the changelog.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| test/unit/core/test_parse.py | Adds parser-level unit tests for probability-bearing instructions, including MR-family noise semantics. |
| src/tsim/core/instructions.py | Removes redundant noise injection from MR-family wrappers to prevent double-counting. |
| CHANGELOG.md | Notes the MR-family double-counting fix in the Unreleased section. |
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Summary
The MR, MRX, MRY channels with finite bit flip probability incorrectly applied two bitflip channels instead of one.
MR,MRX, andMRY