add getter/setter for potential

src/main/java/Vertex.java

@@ -74,4 +74,12 @@ public class Vertex implements Serializable, Comparable<Vertex> {
     public int compareTo(Vertex other) {
         return this.vertexLabel - other.getVertexLabel();
     }
+
+    public Double getPotential() {
+        return potential;
+    }
+
+    public void setPotential(Double potential) {
+        this.potential = potential;
+    }
 }