Nolte, G., Ziehe, A., Nikulin, V. V., Schlögl, A., Krämer, N., Brismar, T., & Müller, K.-R. (2008).
Robustly estimating the flow direction of information in complex physical systems. Physical Review
Letters, 100(23):. doi:10.1103/PhysRevLett.100.234101.