diff --git a/src/tree/model.h b/src/tree/model.h
index 081f71ffb..af99a5145 100644
--- a/src/tree/model.h
+++ b/src/tree/model.h
@@ -42,11 +42,17 @@ class TreeModel {
     int max_depth;
     /*! \brief  number of features used for tree construction */
     int num_feature;
+    /*! 
+     * \brief leaf vector size, used for vector tree
+     * used to store more than one dimensional information in tree
+     */
+    int size_leaf_vector;
     /*! \brief reserved part */
-    int reserved[32];
+    int reserved[31];
     /*! \brief constructor */
     Param(void) {
       max_depth = 0;
+      size_leaf_vector = 0;
       memset(reserved, 0, sizeof(reserved));
     }
     /*! 
@@ -57,6 +63,7 @@ class TreeModel {
     inline void SetParam(const char *name, const char *val) {
       if (!strcmp("num_roots", name)) num_roots = atoi(val);
       if (!strcmp("num_feature", name)) num_feature = atoi(val);
+      if (!strcmp("size_leaf_vector", name)) size_leaf_vector = atoi(val);
     }
   };
   /*! \brief tree node */
@@ -166,10 +173,12 @@ class TreeModel {
  protected:
   // vector of nodes
   std::vector<Node> nodes;
-  // stats of nodes
-  std::vector<TNodeStat> stats;
   // free node space, used during training process
   std::vector<int>  deleted_nodes;
+  // stats of nodes
+  std::vector<TNodeStat> stats;
+  // leaf vector, that is used to store additional information
+  std::vector<bst_float> leaf_vector;
   // allocate a new node,
   // !!!!!! NOTE: may cause BUG here, nodes.resize
   inline int AllocNode(void) {
@@ -184,6 +193,7 @@ class TreeModel {
                  "number of nodes in the tree exceed 2^31");
     nodes.resize(param.num_nodes);
     stats.resize(param.num_nodes);
+    leaf_vector.resize(param.num_nodes * param.size_leaf_vector); 
     return nd;
   }
   // delete a tree node
@@ -247,6 +257,14 @@ class TreeModel {
   inline NodeStat &stat(int nid) {
     return stats[nid];
   }
+  /*! \brief get leaf vector given nid */
+  inline bst_float* leafvec(int nid) {
+    return &leaf_vector[nid * param.size_leaf_vector];
+  }
+  /*! \brief get leaf vector given nid */
+  inline const bst_float* leafvec(int nid) const{
+    return &leaf_vector[nid * param.size_leaf_vector];
+  }
   /*! \brief initialize the model */
   inline void InitModel(void) {
     param.num_nodes = param.num_roots;
diff --git a/src/tree/param.h b/src/tree/param.h
index 5a73c4287..6e02db00a 100644
--- a/src/tree/param.h
+++ b/src/tree/param.h
@@ -145,8 +145,8 @@ struct GradStats {
   double sum_grad;
   /*! \brief sum hessian statistics */
   double sum_hess;
-  /*! \brief constructor */
-  GradStats(void) {
+  /*! \brief constructor, the object must be cleared during construction */
+  explicit GradStats(const TrainParam &param) {
     this->Clear();
   }
   /*! \brief clear the statistics */
@@ -169,29 +169,31 @@ struct GradStats {
   inline double CalcWeight(const TrainParam &param) const {
     return param.CalcWeight(sum_grad, sum_hess);
   }
-  /*!\brief calculate gain of the solution */
+  /*! \brief calculate gain of the solution */
   inline double CalcGain(const TrainParam &param) const {
     return param.CalcGain(sum_grad, sum_hess);
   }
   /*! \brief add statistics to the data */
-  inline void Add(double grad, double hess) {
-    sum_grad += grad; sum_hess += hess;
-  }  
-  /*! \brief add statistics to the data */
   inline void Add(const GradStats &b) {
     this->Add(b.sum_grad, b.sum_hess);
   }
-  /*! \brief substract the statistics by b */
-  inline GradStats Substract(const GradStats &b) const {
-    GradStats res;
-    res.sum_grad = this->sum_grad - b.sum_grad;
-    res.sum_hess = this->sum_hess - b.sum_hess;
-    return res;
+  /*! \brief set current value to a - b */
+  inline void SetSubstract(const GradStats &a, const GradStats &b) {
+    sum_grad = a.sum_grad - b.sum_grad;
+    sum_hess = a.sum_hess - b.sum_hess;
   }
   /*! \return whether the statistics is not used yet */
   inline bool Empty(void) const {
     return sum_hess == 0.0;
   }
+  /*! \brief set leaf vector value based on statistics */
+  inline void SetLeafVec(const TrainParam &param, bst_float *vec) const{
+  }
+ protected:
+  /*! \brief add statistics to the data */
+  inline void Add(double grad, double hess) {
+    sum_grad += grad; sum_hess += hess;
+  }
 };
 
 /*! 
diff --git a/src/tree/updater_colmaker-inl.hpp b/src/tree/updater_colmaker-inl.hpp
index fa13e607c..0a494fb5c 100644
--- a/src/tree/updater_colmaker-inl.hpp
+++ b/src/tree/updater_colmaker-inl.hpp
@@ -51,8 +51,8 @@ class ColMaker: public IUpdater<FMatrix> {
     /*! \brief current best solution */
     SplitEntry best;
     // constructor
-    ThreadEntry(void) {
-      stats.Clear();
+    explicit ThreadEntry(const TrainParam &param)
+        : stats(param) {
     }
   };
   struct NodeEntry {
@@ -65,8 +65,8 @@ class ColMaker: public IUpdater<FMatrix> {
     /*! \brief current best solution */
     SplitEntry best;
     // constructor
-    NodeEntry(void) : root_gain(0.0f), weight(0.0f){
-      stats.Clear();
+    explicit NodeEntry(const TrainParam &param)
+        : stats(param), root_gain(0.0f), weight(0.0f){
     }
   };
   // actual builder that runs the algorithm
@@ -100,6 +100,7 @@ class ColMaker: public IUpdater<FMatrix> {
         p_tree->stat(nid).loss_chg = snode[nid].best.loss_chg;
         p_tree->stat(nid).base_weight = snode[nid].weight;
         p_tree->stat(nid).sum_hess = static_cast<float>(snode[nid].stats.sum_hess);
+        snode[nid].stats.SetLeafVec(param, p_tree->leafvec(nid));
       }
     }
 
@@ -179,9 +180,9 @@ class ColMaker: public IUpdater<FMatrix> {
                             const RegTree &tree) {
       {// setup statistics space for each tree node
         for (size_t i = 0; i < stemp.size(); ++i) {
-          stemp[i].resize(tree.param.num_nodes, ThreadEntry());
+          stemp[i].resize(tree.param.num_nodes, ThreadEntry(param));
         }
-        snode.resize(tree.param.num_nodes, NodeEntry());
+        snode.resize(tree.param.num_nodes, NodeEntry(param));
       }
       const std::vector<bst_uint> &rowset = fmat.buffered_rowset();
       // setup position
@@ -196,7 +197,7 @@ class ColMaker: public IUpdater<FMatrix> {
       // sum the per thread statistics together
       for (size_t j = 0; j < qexpand.size(); ++j) {
         const int nid = qexpand[j];
-        TStats stats; stats.Clear();
+        TStats stats(param);
         for (size_t tid = 0; tid < stemp.size(); ++tid) {
           stats.Add(stemp[tid][nid].stats);
         }
@@ -231,6 +232,8 @@ class ColMaker: public IUpdater<FMatrix> {
       for (size_t j = 0; j < qexpand.size(); ++j) {
         temp[qexpand[j]].stats.Clear();
       }
+      // left statistics
+      TStats c(param);
       while (it.Next()) {
         const bst_uint ridx = it.rindex();
         const int nid = position[ridx];
@@ -246,7 +249,7 @@ class ColMaker: public IUpdater<FMatrix> {
         } else {
           // try to find a split
           if (fabsf(fvalue - e.last_fvalue) > rt_2eps && e.stats.sum_hess >= param.min_child_weight) {
-            TStats c = snode[nid].stats.Substract(e.stats);
+            c.SetSubstract(snode[nid].stats, e.stats);
             if (c.sum_hess >= param.min_child_weight) {
               double loss_chg = e.stats.CalcGain(param) + c.CalcGain(param) - snode[nid].root_gain;
               e.best.Update(loss_chg, fid, (fvalue + e.last_fvalue) * 0.5f, !is_forward_search);
@@ -261,7 +264,7 @@ class ColMaker: public IUpdater<FMatrix> {
       for (size_t i = 0; i < qexpand.size(); ++i) {
         const int nid = qexpand[i];
         ThreadEntry &e = temp[nid];
-        TStats c = snode[nid].stats.Substract(e.stats);
+        c.SetSubstract(snode[nid].stats, e.stats);
         if (e.stats.sum_hess >= param.min_child_weight && c.sum_hess >= param.min_child_weight) {
           const double loss_chg = e.stats.CalcGain(param) + c.CalcGain(param) - snode[nid].root_gain;
           const float delta = is_forward_search ? rt_eps : -rt_eps;
diff --git a/src/tree/updater_refresh-inl.hpp b/src/tree/updater_refresh-inl.hpp
index e0e7ab520..d76936791 100644
--- a/src/tree/updater_refresh-inl.hpp
+++ b/src/tree/updater_refresh-inl.hpp
@@ -44,8 +44,8 @@ class TreeRefresher: public IUpdater<FMatrix> {
       int tid = omp_get_thread_num();
       for (size_t i = 0; i < trees.size(); ++i) {
         std::vector<TStats> &vec = stemp[tid * trees.size() + i];
-        vec.resize(trees[i]->param.num_nodes);
-        std::fill(vec.begin(), vec.end(), TStats());
+        vec.resize(trees[i]->param.num_nodes, TStats(param));
+        std::fill(vec.begin(), vec.end(), TStats(param));
       }
       fvec_temp[tid].Init(trees[0]->param.num_feature);
     }
@@ -114,6 +114,7 @@ class TreeRefresher: public IUpdater<FMatrix> {
     RegTree &tree = *p_tree;
     tree.stat(nid).base_weight = gstats[nid].CalcWeight(param);
     tree.stat(nid).sum_hess = static_cast<float>(gstats[nid].sum_hess);
+    gstats[nid].SetLeafVec(param, tree.leafvec(nid));
     if (tree[nid].is_leaf()) {
       tree[nid].set_leaf(tree.stat(nid).base_weight * param.learning_rate);
     } else {