@misc{
    NDFApackage,
    author = "Valpola, Harri and Honkela, Antti and Giannakopoulos, Xavier",
    url = "http://www.cis.hut.fi/projects/bayes/software/",
    flag = "SOFTWARE",
    year = "2002",
    title = "Nonlinear Dynamical Factor Analysis {M}atlab package"
}