VBsparsePCA             The main function for the variational Bayesian
                        method for sparse PCA
foldednorm.mean         The function for obtaining the mean of a folded
                        normal distribution
spca.cavi.Laplace       Function for the PX-CAVI algorithm using the
                        Laplace slab
spca.cavi.mvn           Function for the PX-CAVI algorithm using the
                        multivariate normal slab
