40 lines
2.2 KiB
Markdown
40 lines
2.2 KiB
Markdown
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# LAC Critical Lessons — NEVER FORGET
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These are hard-won insights from past optimization sessions. Violating any of these will cause failures.
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## NX Safety (CRITICAL)
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- **NEVER kill ugraf.exe directly** → use `NXSessionManager.close_nx_if_allowed()`
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- **PowerShell for NX journals** → NEVER use `cmd /c`
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- **Always load `*_i.prt` before `UpdateFemodel()`** → mesh won't update without the idealized part
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- **File chain must be intact:** `.sim → .fem → *_i.prt → .prt` (ALL must be present)
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## Optimization (CRITICAL)
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- **CMA-ES doesn't evaluate x0 first** → always call `enqueue_trial(x0)` to evaluate baseline
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- **Surrogate + L-BFGS = DANGEROUS** → gradient descent finds fake optima on surrogate surface
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- **NEVER rewrite `run_optimization.py` from scratch** → ALWAYS copy a working template (V15 NSGA-II is gold standard)
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- **Relative WFE math:** use `extract_relative()` (node-by-node subtraction) → NOT `abs(RMS_a - RMS_b)` (wrong math!)
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## File Management (IMPORTANT)
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- **Trial folders:** `trial_NNNN/` — zero-padded, never reused, never overwritten
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- **Always copy working studies** — never modify originals
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- **Output paths must be relative** — no absolute Windows/Linux paths (Syncthing-compatible)
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- **Never delete trial data mid-run** — archive after study is complete
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## Algorithm Selection (REFERENCE)
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| Variables | Landscape | Recommended | Notes |
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|-----------|-----------|-------------|-------|
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| < 5 | Smooth | Nelder-Mead or COBYLA | Simple, fast convergence |
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| 5-20 | Noisy | CMA-ES | Robust, population-based |
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| > 20 | Any | Bayesian (Optuna TPE) | Efficient with many variables |
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| Multi-obj | Any | NSGA-II or MOEA/D | Pareto front generation |
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| With surrogate | Expensive eval | GNN surrogate + CMA-ES | Reduce simulation count |
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## Common Failures
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| Symptom | Cause | Fix |
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|---------|-------|-----|
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| Mesh not updating | Missing `*_i.prt` load | Load idealized part first |
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| NX crashes on journal | Using `cmd /c` | Switch to PowerShell |
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| Baseline trial missing | CMA-ES skips x0 | Explicitly enqueue baseline |
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| Optimization finds unphysical optimum | Surrogate + gradient | Switch to CMA-ES or add validation |
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| Study can't resume | Absolute paths in script | Use relative paths |
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