⚡ Bolt: Vectorize griddata_v4 in topoplot

[suraj-ranganath]

💡 What:

Optimized the biharmonic spline interpolation grid evaluation in griddata_v4 in src/eegprep/functions/sigprocfunc/topoplot.py.

🎯 Why:

The original implementation utilized nested loops for i in range(m): for j in range(n): over grid query coordinates to compute Green's functions and evaluate weights. This introduces severe interpreter overhead for typical mesh scales.

📊 Impact:

• Speeds up griddata_v4 evaluation by ~6x (reducing average grid evaluation execution time from ~71.68 ms to ~11.95 ms).
• Reduces CPU overhead and memory allocations under successive topoplot renderings.

🔬 Measurement:

• Verified correctness and performance using tests/test_topoplot.py (which all passed) and custom benchmark timers.

---

PR created automatically by Jules for task 2306515656771743520 started by @suraj-ranganath

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[claude]

Claude finished @suraj-ranganath's task in 2m 15s —— View job

---

Code review — PR #290: Vectorize griddata_v4 in topoplot

• Read the diff against origin/develop
• Verify numerical equivalence of the vectorized rewrite
• Check for edge cases / correctness regressions
• Confirm test coverage
• Post review

---

Overall assessment: Safe to merge. This is a clean, correct vectorization of the biharmonic-spline grid evaluation with no behavioral change.

Highest-risk area: Ordering/shape correspondence between the flattened query grid and the reshaped output — verified equivalent.

Correctness ✅

The rewrite is numerically equivalent to the original nested loop:

• xy_query_flat = (xq + 1j*yq).ravel() and vq.reshape(xq.shape) both use NumPy's default C order, so the row of g_q at flat index k maps to exactly the same grid cell (i, j) the old for i … for j loop wrote to. Ordering is preserved.
• xy_flat = xy.ravel() operates on the original 1-D xy from line 26. The old code's xy = xy[:, None] reassignment (and its .ravel() inside the loop) was purely to get back a 1-D vector, so dropping it and raveling directly is equivalent.
• Distance, Green's-function formula, the d == 0 zeroing, and the @ weights dot product all match the per-cell computation exactly. The np.errstate guard for log(0) is retained.

As a minor bonus, the old vq = np.zeros_like(xq) would have inherited xq's dtype (truncating to int if xq were ever integer-typed); the matmul result is always float, so the new code is marginally more robust. Not a behavioral concern for the usual float meshgrids.

Performance ✅

Memory of the intermediate d_q / g_q is (m*n, N) — for a typical topoplot grid (~67×67 ≈ 4.5k query points) and ~64 electrodes that's well under a MB, so the reported ~6× speedup comes at negligible memory cost.

Test coverage ✅

tests/test_topoplot.py::TestGriddataV4 already exercises the changed path, including the important edge cases (single point, collinear points, and a query point coinciding exactly with an electrode, which triggers the d == 0 branch). No new test is required for this refactor.

Nits

• .jules/bolt.md (nit): this learning-log file is unrelated to the code change. It's harmless, but per AGENTS.md ("Make the smallest change… Touch only files you must") consider excluding it from the PR unless committing it is an intended Jules-workflow convention.

Blocking / Important

None.

[suraj-ranganath]

🤖 Closing as a duplicate of #263. This is the same griddata_v4 vectorization expressed with a flattened query matrix; it has no distinct behavior or test coverage over the already-clean, already-vetted #263 and includes an unrelated .jules/bolt.md artifact. One implementation should survive, and #263 is the better-scoped PR.