use best_b, best_k1

app.py

@@ -192,8 +192,8 @@ class BM25Index(InvertedIndex):
         output_dir: Optional[str] = None,
         ndocs: Optional[int] = None,
         show_progress_bar: bool = True,
-        k1: float = 0.9,
-        b: float = 0.4,
+        k1: float = 0.8,
+        b: float = 0.6,
     ) -> BM25Index:
         # Counting TFs, DFs, doc_lengths, etc.:
         counting = run_counting(