A conditional symmetric memristive system with amplitude and frequency control Zhenyu Gu, Chunbiao Li, Xiaofang Pei, Changyuan Tao and Zuohua Liu Eur. Phys. J. Special Topics, 229 6-7 (2020) 1007-1019 Published online: 26 March 2020 DOI: 10.1140/epjst/e2020-900185-y