See the Julia session below: julia> using FractionalDiffEq, Plots julia> function sys!(du, u, p, t) du[1] = -0.05*u[2] - 0.05*u[3] + 0.01*tanh(u[2]) du[2] = 0.05*u[1] + 0.02*u[2] + 0.01*tanh(u[1]) du[3] = 0.1 - 0.2*u[3] + 0.05*u[1]*u[3] + 0.01*tanh(u[3]) end sys! (generic function with 1 method) julia> prob = FractionalDsicreteSystem(sys!, 0.98, [1, -1, 0]) ERROR: UndefVarError: `FractionalDsicreteSystem` not defined Stacktrace: [1] top-level scope @ REPL[3]:1 julia> result = solve(prob, 7, GL()) ERROR: UndefVarError: `prob` not defined Stacktrace: [1] top-level scope