Capping negative boost at 0.5 (#622)

backend/danswer/datastores/datastore_utils.py

@@ -6,13 +6,19 @@
 
 
 DEFAULT_BATCH_SIZE = 30
-BOOST_MULTIPLIER = 2  # Try to keep this consistent with Vespa
 
 
 def translate_boost_count_to_multiplier(boost: int) -> float:
-    # Sigmoid function, maxed out at BOOST_MULTIPLIER
-    # 3 here stretches it out so we hit asymptote slower
-    return BOOST_MULTIPLIER / (1 + math.exp(-1 * boost / 3))
+    """Mapping boost integer values to a multiplier according to a sigmoid curve
+    Piecewise such that at many downvotes, its 0.5x the score and with many upvotes
+    it is 2x the score. This should be in line with the Vespa calculation."""
+    # 3 in the equation below stretches it out to hit asymptotes slower
+    if boost < 0:
+        # 0.5 + sigmoid -> range of 0.5 to 1
+        return 0.5 + (1 / (1 + math.exp(-1 * boost / 3)))
+
+    # 2 x sigmoid -> range of 1 to 2
+    return 2 / (1 + math.exp(-1 * boost / 3))
 
 
 def get_uuid_from_chunk(

backend/danswer/datastores/vespa/app_config/schemas/danswer_chunk.sd

@@ -100,9 +100,9 @@ schema danswer_chunk {
         }
 
         function inline document_boost() {
-            # 0 to 2x score following sigmoid function stretched out by factor of 3
+            # 0.5 to 2x score: piecewise sigmoid function stretched out by factor of 3
             # meaning requires 3x the number of feedback votes to have default sigmoid effect
-            expression: 2 / (1 + exp(-attribute(boost) / 3))
+            expression: if(attribute(boost) < 0, 0.5 + (1 / (1 + exp(-attribute(boost) / 3))), 2 / (1 + exp(-attribute(boost) / 3)))
         }
 
         function inline document_age() {