Mike Klaas Mark Briers Nando de Freitas Arnaud Doucet Simon Maskell Dustin Lang Fast particle smoothing: if I had a million particles. 481-488 2006 conf/icml/2006 ICML https://doi.org/10.1145/1143844.1143905 db/conf/icml/icml2006.html#KlaasBFDML06