Fix bugs in computing center

dtree_learner.py

@@ -13,7 +13,7 @@ def construct_sample_to_feature_func(lin_trans):
         assert len(sample) == STATE_DIM + PERC_DIM
         state = sample[0: STATE_DIM]
         perc = sample[STATE_DIM: STATE_DIM+PERC_DIM]
-        perc_bar = perc - np.dot(state, a_mat.T) + b_vec
+        perc_bar = perc - (np.dot(state, a_mat.T) + b_vec)
         return perc_bar
     return sample_to_feature_vec