Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch|Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch|Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch|Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch|Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch|Seminar for Statistics, Department of Mathematics, ETH Zurich, 8092 Zurich, Switzerland. stekhoven@stat.math.ethz.ch