added relative knowledge loss function

app/models/proxy_exercise.rb

@@ -24,4 +24,47 @@ class ProxyExercise < ActiveRecord::Base
       title
     end
 
+    def selectMatchingExercise(user)
+      assigned_user_proxy_exercise = user_proxy_exercise_exercises.where(user: user).first
+      recommendedExercise =
+        if (assigned_user_proxy_exercise)
+          Rails.logger.info("retrieved assigned exercise for user #{user.id}: Exercise #{assigned_user_proxy_exercise.exercise}" )
+          assigned_user_proxy_exercise.exercise
+        else
+          Rails.logger.info("find new matching exercise for user #{user.id}" )
+          matchingExercise = findMatchingExercise(user)
+          user.user_proxy_exercise_exercises << UserProxyExerciseExercise.create(user: user, exercise: matchingExercise, proxy_exercise: self)
+          matchingExercise
+        end
+      recommendedExercise
+    end
+
+    def findMatchingExercise(user)
+      exercises.shuffle.first
+    end
+
+    def score(user, ex)
+      1
+    end
+
+    def getRelativeKnowledgeLoss(user, execises)
+      # initialize knowledge for each tag with 0
+      topic_knowledge_loss_user = Tag.all.map{|t| [t, 0]}.to_h
+      topic_knowledge_max = Tag.all.map{|t| [t, 0]}.to_h
+      execises.each do |ex|
+        score = score(user, ex)
+        ex.tags.each do |t|
+          tag_ratio = ex.exercise_tags.where(tag: t).factor / ex.exercise_tags.inject(0){|sum, et| sum += et.factor }
+          topic_knowledge = ex.expected_difficulty * tag_ratio
+          topic_knowledge_loss_user[t] += (1-score) * topic_knowledge
+          topic_knowledge_max[t] += topic_knowledge
+        end
+      end
+      relative_loss = {}
+      topic_knowledge_max.keys.each do |t|
+        relative_loss[t] = topic_knowledge_loss_user[t] / topic_knowledge_max[t]
+      end
+      relative_loss
+    end
+
 end