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Update parameter tying investigation with paramz dependency analysis

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Neil Lawrence 2025-08-15 11:24:42 +02:00
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backlog/infrastructure/2025-08-15_parameter-tying-framework.md
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@ -77,12 +77,33 @@ Task created after identifying parameter tying as a potential limitation during
### 2025-08-15 (GitHub Investigation)
Found existing GitHub issues confirming parameter tying limitations:
**GPy Issues:**
- **Issue #462 (2016)**: "tie_params doesnt work ?" - `AttributeError: 'Add' object has no attribute 'tie_params'`
- **Issue #789 (2019)**: "Non-implemented Param tying work-around options" - Confirms `tie_to` from Parametrized is not implemented
- **Issue #878 (2020)**: "Constraining hyperparameters" - Open issue requesting parameter equality constraints in MultioutputGP
**Paramz Issues:**
- **Issue #34 (2019)**: "What does m.name[0].tie_to(other) do?" - `tie_to` is documented but not implemented
- **Issue #35 (2020)**: "Constraint that makes parameters sum to one?" - Also references missing `tie_to` functionality
**Key Findings:**
- Parameter tying functionality has been missing/broken in GPy for at least 5 years
- Parameter tying functionality has been missing/broken in both GPy and paramz for at least 5 years
- `tie_to` method is documented in paramz but not implemented
- Multiple users have requested this feature for different use cases
- Current workarounds involve manual parameter management
- No systematic solution exists in the codebase
- No systematic solution exists in either codebase
- The problem is deeper than just GPy - it's a fundamental limitation in the paramz framework
### 2025-08-15 (Paramz Dependency Analysis)
**Current State:**
- GPy still actively depends on paramz: `"paramz>=0.9.6"` in setup.py
- No evidence of plans to remove paramz dependency
- Recent paramz-related work: Issue #978 (2022) fixing broken kernels due to `add_parameter` → `link_parameter` rename
**Implications for Parameter Tying:**
- **Option 1**: Fix paramz first - implement `tie_to` in paramz framework
- **Option 2**: Work around paramz - create parameter tying within GPy without relying on paramz's missing features
- **Option 3**: Replace paramz - major migration away from paramz (unlikely given current dependency)
**Recommendation**: Focus on Option 1 or 2, as paramz remains actively maintained and GPy continues to depend on it.