Fig. 1. Illustration of “learning-forgetting-relearning” experiment: (a) The applied voltage in each period of this experiment; (b)−(d) the change of memristor memory during the first learning process, forgetting process, and the memory recovery period of relearning process, respectively.N_L, t_f, and N_R stand for the number of applied pulses in the first learning process, the forgetting time, and the number of applied pulses in the memory recovery period of the relearning process, respectively. “学习-遗忘-再学习”实验过程的示意说明　(a) 实验各个阶段施加在忆阻器上的电压; (b)−(d) 依次为初次学习过程、遗忘过程、再次学习的记忆恢复过程中忆阻器记忆的变化情况, 横坐标中N_L, t_f, N_R分别表示初次学习的脉冲数量、遗忘过程的时长、再次学习的记忆恢复过程所经历的脉冲数量

Fig. 2. Curves of (a) F_w and (b) T_w with respect to V, b₊ = b_– = 35. (a) F_w和 (b) T_w关于V的曲线, b₊ = b_– = 35

Fig. 3. Variation of w within a pulse period when w_min and τ_w0 take different values: (a) Variation of w when τ_w0 = 0.2 s and w_min takes different values; (b) variation of w when w_min = 0.2 and τ_w0 takes different values. w_min和τ_w0的大小对状态变量w在一个脉冲周期内的变化情况的影响　(a) τ_w0 = 0.2 s, w_min取值为不同常数时w的变化情况; (b) w_min = 0.2, τ_w0取值为不同常数时w的变化情况

Fig. 4. Influence of the initial value of τ_w0 on the variation of w in “learning-forgetting- relearning” process. The maximum value of w during the first learning period is marked by a dashed line: (a) The initial value of τ_w0 is 0.01 s; (b) the initial value of τ_w0 is 1 s. 状态变量τ_w0的初值大小对于“学习-遗忘-再学习”过程中w的变化的影响, 虚线标明初次学习阶段w所达到的最大值(a) τ_w0初值为0.01 s; (b) τ_w0初值为1 s

Fig. 5. Simulations of “learning-forgetting-relearning” process when τ_w+ = 0.06 s, τ_max+ = 0.05 s, and τ_min+ takes different values: (a) τ_min+ = 0.5 s; (b) τ_min+ = 0.2 s; (c) τ_min+ = 0.1 s. The maximum value of w during the first learning period is marked by a dashed line. τ_w+ = 0.06 s, τ_max+ = 0.05 s, τ_min+取不同值时的“学习-遗忘-再学习”实验仿真结果　(a) τ_min+ = 0.5 s; (b) τ_min+ = 0.2 s; (c) τ_min+ = 0.1 s. 虚线标出w在初次学习阶段所达到的最大值

Fig. 6. Simulations of “learning-forgetting-relearning” process when τ_min+ = 0.2 s, τ_max+ = 0.1 s, and τ_w+ takes different values: (a) τ_w+ = 0.15 s; (b) τ_w+ = 0.06 s; (c) τ_w+ = 0.01 s. The maximum value of w during the first learning period is marked by a dashed line. τ_min+ = 0.2 s, τ_max+ = 0.1 s, τ_w+取不同值时的“学习-遗忘-再学习”实验仿真结果　(a) τ_w+ = 0.15 s; (b) τ_w+ = 0.06 s; (c) τ_w+ = 0.01 s. 虚线标出w在初次学习阶段所达到的最大值

Fig. 7. Simulations of “learning-forgetting-relearning” process when τ_w+ = 0.15 s, τ_min+ = 0.1 s, and τ_max+ takes different values: (a) τ_max+ = 0.1 s; (b) τ_max+ = 0.05 s; (c) τ_max+ = 0.003 s; (d) simulation of “learning-forgetting-relearning” process when w_max = 1, and other parameters are the same as those used in (a)−(c). The maximum value ofw during the first learning period is marked by a dashed line. τ_w+ = 0.15 s, τ_min+ = 0.1 s, τ_max+取不同值时的“学习-遗忘-再学习”实验仿真结果　(a) τ_max+ = 0.1 s; (b) τ_max+ = 0.05 s; (c) τ_max+ = 0.003 s; (d) 当w_max为常数1, 模型其他参数与(a)−(c)相同时的“学习-遗忘-再学习”实验仿真结果. 虚线标出w在初次学习阶段所达到的最大值

Fig. 8. Change of the conductive channel and its surrounding area during different periods of the “learning-forgetting-relearning” process: (a) The first learning process; (b) the forgetting process; (c) the memory recovery period of the relearning process.忆阻器两电极间导电通道及其周围区域在“学习-遗忘-再学习”实验中的变化情况　(a) 初次学习阶段; (b) 遗忘阶段; (c) 再次学习的记忆恢复阶段

Table 1. Experimental data of “learning-forgetting-relearning” experiment in References [21—30].