Add err scorer

db/migrate/20250107195202_add_err.rb

@@ -0,0 +1,12 @@
+class AddErr < ActiveRecord::Migration[8.0]
+  def change
+    Scorer.where(name: 'ERR@10').first_or_create(
+      scale:              (0..3).to_a,
+      scale_with_labels:  {"0":"Poor","1":"Fair","2":"Good","3":"Perfect"},
+      show_scale_labels:  true,
+      code:               File.readlines('./db/scorers/[email protected]','\n').join('\n'),
+      name:               'ERR@10',
+      communal:           true
+    )    
+  end
+end

db/scorers/err@10.js

@@ -0,0 +1,31 @@
+let k = 10 // @Rank
+// if less than K results, need to reduce K now or final score is too low
+k = numReturned() < k ? numReturned() : k
+const scores = Array(k);
+const missing_rating = 0; // pessimistic assumption
+let i = 0
+for (i = 0; i < k; i++) {
+  if (hasDocRating(i)) {
+    scores[i] = (docRating(i));
+  } else {
+    scores[i] = missing_rating;
+  }
+}
+
+function gain(grade, maxGrade) {
+    return (Math.pow(2,grade) - 1.0)/Math.pow(2,maxGrade)
+}
+function err(lst) {
+    let ERR = 0.0
+    let trust = 1.0
+    for (i = 0; i < lst.length; i++) {
+        const rank = i + 1.0
+	// max is the maximum possible rating for the scorer.
+        const pUseful = gain(lst[i], max)
+        const disc = pUseful/rank
+        ERR = ERR + trust * disc
+        trust = trust * (1.0 - pUseful)
+    }
+    return ERR
+}
+setScore(err(scores))

db/seeds.rb

@@ -60,6 +60,15 @@
   communal:           true
 )
 
+Scorer.where(name: 'ERR@10').first_or_create(
+  scale:              (0..3).to_a,
+  scale_with_labels:  {"0":"Poor","1":"Fair","2":"Good","3":"Perfect"},
+  show_scale_labels:  true,
+  code:               File.readlines('./db/scorers/[email protected]','\n').join('\n'),
+  name:               'ERR@10',
+  communal:           true
+)
+
 SelectionStrategy.where(name: 'Single Rater').first_or_create(
   name: 'Single Rater',
   description: 'A single rating for each query/doc pair is all that is required.  The fastest way to get a lot of ratings, with lower quality.'