The reducer of restricted Boltzmann machine (RBM) training part in deep learning MapReduce program

/*
 * Project Name: Deep learning based on Hadoop (MapReduce)
 * 
 * Class Description: 
 * 	This is the reducer of restricted Boltzmann machine (RBM) training part in deep learning MapReduce program.
 *  The task of this MapReduce is to train the rbm between two layers in unsupervised way,
 *  and output the updated weight.
 *  
 *  Each reducer collect all the weight updates from one single weight ID. 
 *  It adds the updates from the same weight up and write to the final output.
 * 
 * 
 * Author: Kairan Sun
 * Last Update Date: Nov. 30, 2013 
 */