(a) The globally optimal control u(I) for six η-values. The dashed lines are for illustration purpose only. (b) The actual controls A(I) with fixed β- and six α-values, under the limit condition K = 0. The α-values are specially chosen to render an exact match with (a). The solid and dashed lines indicate stable and unstable branches, respectively. (c) The same controls but with K = 10−4. (d) The same controls but with K = 10−2. (e) Under the condition K = 0, the solutions to electronic supplementary material, equation (S40) reduce to three straight lines, which constitute a bistable switch with Ion = cβ−1 and ΔI = cα. (f) Under the condition K = 0, the actual controls A(I) with fixed α- and four β-values.