A listed landfill's share a rounding error below zero sends no negative waste

SWEET_python/advanced_dst_city.py

@@ -737,7 +737,10 @@ def _with_other_landfills(request: AdvancedDSTCityRequest) -> AdvancedDSTCityReq
     rows: Dict[str, Dict[int, List[float]]] = {}
     for variant in variants:
         _validate_share_range(splits[variant], variant)
-        listed = splits[variant].where(accepting[variant], 0.0)
+        # The range check tolerates a share a rounding error outside [0, 1]. Used
+        # as given, -0.01 would bury negative waste at that site and hand other
+        # landfills 101% of the rest.
+        listed = splits[variant].where(accepting[variant], 0.0).clip(lower=0.0, upper=1.0)
         claimed = listed.sum(axis=1)
         over = claimed > 1.0
         listed.loc[over] = listed.loc[over].div(claimed[over], axis=0)

changelog/2026-10.md

@@ -195,6 +195,11 @@ take to other landfills, so a caller no longer has to make the shares add up to
 
 ## Fixed
 
+- **A listed landfill's share a rounding error below zero sends no negative waste.**
+  With `other_landfills`, a share the range check tolerates (down to -0.02) was used
+  as given: -0.01 buried negative waste at that site and gave other landfills 101%
+  of the rest. Tolerated shares are now clipped to [0, 1] first.
+
 - **Indonesia has a per-capita waste rate of its own** (model-output change).
   `defaults_2019.msw_per_capita_country` copies IPCC 2019 Refinement, Vol. 5
   Ch. 2, Table 2A.1 (Updated), 2010 column, in tonnes per person per year. All

tests/test_adst_city_other_landfills.py

@@ -214,6 +214,18 @@ def test_shares_over_one_are_scaled_down_and_other_landfills_take_nothing():
     assert shares[2].to_numpy() == pytest.approx(0.0)
 
 
+def test_a_tolerated_negative_share_sends_no_negative_waste_anywhere():
+    """-0.01 passes the range check as a rounding error. Used as given, it buried
+    negative waste at the listed site and gave other landfills 101% of the rest."""
+    result = _run(_request([_site()], [-0.01], other=_other()))
+
+    for variant in ("baseline", "scenario"):
+        shares = _site_shares(result, variant)
+        assert shares[0].to_numpy() == pytest.approx(0.0)
+        assert shares[1].to_numpy() == pytest.approx(1.0)
+        assert (pd.concat(result["mass_flow"][variant]["sites"], axis=1) >= 0).all().all()
+
+
 def test_other_landfills_open_with_a_listed_site_that_opens_before_the_model():
     early = MODEL_START_YEAR - 10
     shares = _site_shares(