<NME> Density.java
<BEF> ADDFILE
<MSG> speed up

<DFF> @@ -0,0 +1,8 @@
+package edu.neu.ccs.pyramid.dataset;
+
+/**
+ * Created by chengli on 3/6/17.
+ */
+public enum Density {
+    DENSE, SPARSE_RANDOM, SPARSE_SEQUENTIAL
+}

speed up