Neutral element for sum is [0, 0]

2 files changed, 11 insertions, 2 deletions

diff --git a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
index f5bd2efc..66dcb00f 100644
--- a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
+++ b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
@@ -21,6 +21,11 @@ public enum IntervalAggregationMode implements BinaryOperator<Interval> {
                                 }
                         };
                 }
+                
+                @Override
+                public Interval getNeutral() {
+                        return Interval.ZERO;
+                }
         },
 
         JOIN("intervalJoin", "Calculate the smallest interval containing all the intervals in a set") {
@@ -63,4 +68,8 @@ public enum IntervalAggregationMode implements BinaryOperator<Interval> {
         }
 
         public abstract IntervalRedBlackNode createNode(Interval interval);
+        
+        public Interval getNeutral() {
+                return Interval.EMPTY;
+        }
 }
diff --git a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
index 940c71bb..21d3d73b 100644
--- a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
+++ b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
@@ -36,13 +36,13 @@ class IntervalAggregationOperator implements IMultisetAggregationOperator<Interv
 
         override getAggregate(IntervalRedBlackNode result) {
                 if (result.leaf) {
-                        null
+                        mode.neutral
                 } else {
                         result.result
                 }
         }
 
         override aggregateStream(Stream<Interval> stream) {
-                stream.reduce(mode).orElse(null)
+                stream.reduce(mode).orElse(mode.neutral)
         }
 }