Kentaro Hirata Hideki Kokame Stability analysis of linear systems with state jump - motivated by periodic motion control of passive walker. 949-953 2003 CCA https://doi.org/10.1109/CCA.2003.1223138 conf/IEEEcca/2003 db/conf/IEEEcca/IEEEcca2003.html#HirataK03 streams/conf/IEEEcca