“…Actually, symmetry of such chaotic system means symmetry of the solutions of system equations, which is the essential reason that coexisting attractors appear in pairs symmetrically (Leutcho et al, 2018). Interestingly, the above phenomenon lies not only in general nonlinear chaotic systems (Chen et al, 2016;Li et al, 2017d;Li and Sprott, 2017b;Leutcho et al, 2018) but also in chaotic systems based on the nonlinear devices of memristor (Peng and Min, 2017;Li et al, 2017a;Wang et al, 2018;Li et al, 2019c), memcapacitor (Yuan et al, 2016) and meminductor (Xu et al, 2017), and even in neural network system (Bao et al, 2019a). For a three-dimensional asymmetric chaotic system with a single attractor, the operation of attractor doubling in three dimensions can produce four pairs of symmetric coexisting attractors, and during this process, the symmetry of the constructed model is an important consideration necessarily (Li et al, 2019a).…”