Update libmultilabel/linear/tree.py

Co-authored-by: Chih-Jen Lin <cjlin@csie.ntu.edu.tw>

Author: ericliu8168

libmultilabel/linear/tree.py

@@ -225,7 +225,7 @@ def collect_stat(node: Node):
     root.dfs(collect_stat)
 
     # 16 is because when storing sparse matrices, indices (int64) require 8 bytes and floats require 8 bytes
-    # 2/3 is because that dual coordinate descent method can further get a sparse model vector to save space
+    # Our study showed that among the used features of every binary classification problem, on average no more than 2/3 of weights obtained by the dual coordinate descent method are non-zeros.
     return total_num_weights * 16 * 2/3