Héctor Ríos Jorge Dávila 0001 Leonid M. Fridman Denis V. Efimov State estimation for linear switched systems with unstable invariant zeros and unknown inputs. 5499-5504 2012 CDC https://doi.org/10.1109/CDC.2012.6426455 conf/cdc/2012 db/conf/cdc/cdc2012.html#RiosDFE12