logarithmic space mode: pure_root gains space='x'|'log' (default reproduces the published grid bit-for-bit), u = sign(x-c)*log1p(|x-c|/xtol) with c = the end of smaller |f| and s = xtol fixed by derivation; gates G1/G2' pinned by tests/test_log_space.py (7 green); sweep writes the log grid to its OWN sweep_log.json so the verified sweep_full.json is untouched

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

sweep_full.py

@@ -101,20 +101,27 @@ BASELINES = {
 
 
 def make_method(spec):
-    """spec is ('base', name) or ('pure', similarity, scale, guard)."""
+    """spec is ('base', name) or ('pure', similarity, scale, guard[, space]).
+
+    The optional 5th element is the SPACE the step is read in (PREREG
+    amendment 1, 2026-09-20): omitted or "x" reproduces the published grid
+    bit-for-bit, "log" is the logarithmic-march mode."""
     if spec[0] == "base":
         return BASELINES[spec[1]]
-    _, sim, scale, guard = spec
+    sim, scale, guard = spec[1], spec[2], spec[3]
+    space = spec[4] if len(spec) > 4 else "x"
 
     def m(f, a, b, xtol, maxfev):
         return pure_root(f, a, b, xtol, maxfev, similarity=sim,
-                         scale=scale, guard=guard)
+                         scale=scale, guard=guard, space=space)
     return m
 
 
 def label(spec):
     if spec[0] == "base":
         return spec[1]
+    if len(spec) > 4 and spec[4] != "x":
+        return f"{spec[4]}.{spec[1]}.{spec[2]}.{spec[3]}"
     return f"pure.{spec[1]}.{spec[2]}.{spec[3]}"
 
 
@@ -152,6 +159,16 @@ def evaluate(spec):
     return res
 
 
+def build_grid_log(smoke):
+    """The logarithmic-space grid (PREREG 2026-09-20). Baselines are NOT recomputed:
+    their numbers are already in sweep_full.json and re-running known expensive
+    controls is waste. Only the derived scales are admissible in u-space."""
+    sims = ["ratio", "cbrt"] if smoke else sorted(PURE_SIMS)
+    guards = ("credit", "project") if smoke else GUARD_MODES
+    return [("pure", sim, sc, gu, "log")
+            for sim in sims for sc in ("derived", "derived3") for gu in guards]
+
+
 def build_grid(smoke):
     specs = [("base", nm) for nm in BASELINES]
     sims = sorted(PURE_SIMS)
@@ -171,10 +188,11 @@ def build_grid(smoke):
 
 def main():
     smoke = "--smoke" in sys.argv
-    specs = build_grid(smoke)
+    logmode = "--log" in sys.argv          # the u-space grid, written to its OWN file
+    specs = build_grid_log(smoke) if logmode else build_grid(smoke)
     t0 = time.time()
     print(f"sweep: {len(specs)} configurations x 199 problems "
-          f"({'SMOKE' if smoke else 'FULL'})", flush=True)
+          f"({'SMOKE' if smoke else 'FULL'}{', LOG-SPACE' if logmode else ''})", flush=True)
 
     workers = max(1, min(8, (os.cpu_count() or 2) - 1))
     with Pool(workers) as pool:
@@ -185,7 +203,10 @@ def main():
                 print(f"  {i}/{len(specs)} done, "
                       f"{time.time() - t0:.0f}s elapsed", flush=True)
 
-    out = "sweep_smoke.json" if smoke else "sweep_full.json"
+    # the published sweep_full.json is what verify_article.py checks the paper
+    # against, so the log grid never writes into it
+    out = ("sweep_log_smoke.json" if smoke else "sweep_log.json") if logmode else \
+          ("sweep_smoke.json" if smoke else "sweep_full.json")
     with open(out, "w", encoding="utf8") as fh:
         json.dump(results, fh)
     print(f"\nwrote {out}  ({time.time() - t0:.0f}s total)\n", flush=True)
@@ -225,7 +246,7 @@ def report(results, top=20):
             for r in results:
                 if r["spec"][0] != "pure":
                     continue
-                _, sim, sc, gu = r["spec"]
+                sim, sc, gu = r["spec"][1], r["spec"][2], r["spec"][3]
                 if sc != scale or gu != "step" or sim not in group:
                     continue
                 cnt += 1