tokens: In line with the above - presented studies , the goal of the present paper is i ) to provide an extensive comparison of several autoencoder architectures including shallow , deep , recurrent and variational autoencoders , with a systematic comparison to a linear dimensionality reduction technique , in the present case Principal Component Analysis ( PCA ) ( to the best of our knowledge , such comparison of non - linear approaches with a linear one has never been done in previous studies ) .