Quasi-objective nonlinear principal component analysis.

By means of mathematical analysis and numerical experimentation, this study shows that the problems of non-uniqueness of solutions and data over-fitting, that plague the multilayer feedforward neural network for NonLinear Principal Component Analysis (NLPCA), are caused by inappropriate architecture of the neural network. A simplified two-hidden-layer feedforward neural network, which has no encoding layer and no bias term in the mathematical definitions of bottleneck and output neurons, is proposed to conduct NLPCA. This new, compact NLPCA model alleviates the aforementioned problems encountered when using the more complex neural network architecture for NLPCA. The numerical experiments are based on a data set generated from a well-known nonlinear system, the Lorenz chaotic attractor. Given the same number of bottleneck neurons or reduced dimensions, the compact NLPCA model effectively characterizes and represents the Lorenz attractor with significantly fewer parameters than the relevant three-hidden-layer feedforward neural network for NLPCA.