I understand how an artificial neural network (ANN), can be trained in a supervised manner using backpropogation to improve the fitting by decreasing the error in the predictions. I have heard that an ANN can be used for unsupervised learning but how can this be done without a cost function of some sort to guide the optimization stages? With k-means or the EM algorithm there is a function for which each iteration searches to increase.
- How can we do clustering with an ANN and what mechanism does it use to group data points in the same locality?
(and what extra capabilities are brought with adding more layers to it?)
