Esa Ollila Hannu Oja Visa Koivunen Complex-valued ICA based on a pair of generalized covariance matrices. 3789-3805 2008 52 Computational Statistics & Data Analysis 7 http://dx.doi.org/10.1016/j.csda.2008.01.001 db/journals/csda/csda52.html#OllilaOK08