Probabilistic and Statistical Inference Group, Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada M5S 3G4. jim@psi.toronto.edu|Probabilistic and Statistical Inference Group, Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada M5S 3G4. jim@psi.toronto.edu|Probabilistic and Statistical Inference Group, Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada M5S 3G4. jim@psi.toronto.edu|Probabilistic and Statistical Inference Group, Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada M5S 3G4. jim@psi.toronto.edu