I wrote an article titled “Neural Network Dropout Training” in the May 2014 issue of Visual Studio Magazine. See http://visualstudiomagazine.com/articles/2014/05/01/neural-network-dropout-training.aspx.
Dropout training is a relatively new technique. The purpose is to avoid over-fitting — a situation where training generates weights and bias values so that the neural network predicts with very high accuracy (often 100%) on the training data, but when the NN model is presented with new, non-training data, the model gives very poor accuracy.
Although there are a handful of papers available on the Internet that explain the theory of dropout training, I couldn’t find any concrete examples of how to actually implement the technique. So, I figured it out myself.
The idea of dropout is simple: During the training process, as each data item is presented, a random 50% of the hidden nodes and their connections are dropped from the neural network. This prevents the hidden nodes from co-adapting with each other, forcing the model to rely on only a subset of the hidden nodes. This makes the resulting neural network more robust. Another way of looking at dropout training is that dropout generates many different virtual subsets of the original neural network and then these subsets are averaged to give a final network that generalizes well.