Adding setter method for AVLTreeDigest gen object

core/src/main/java/com/tdunning/math/stats/AVLTreeDigest.java

@@ -27,7 +27,7 @@
 import static com.tdunning.math.stats.IntAVLTree.NIL;
 
 public class AVLTreeDigest extends AbstractTDigest {
-    final Random gen = new Random();
+    Random gen = new Random();
     private final double compression;
     private AVLGroupTree summary;
 
@@ -47,6 +47,17 @@ public AVLTreeDigest(double compression) {
         summary = new AVLGroupTree(false);
     }
 
+    /**
+     * Sets the random object for random number generation purposes.
+     * In cases where a reproducible tree should be created, this function may be used to make the
+     * randomness in this AVLTree become more deterministic.
+     *
+     * @param rand Random object to use for RNG purposes
+     */
+    public void setRandom(Random rand) {
+        gen = rand;
+    }
+
     @Override
     public TDigest recordAllData() {
         if (summary.size() != 0) {