I calculate lyapunov spectrum and it don’t have zero exponent. How i can it fix? I tried change intregrator from RK4 on Tsit5 and Vern9 and it don’t help. Also increase time of integrate don’t help

```
function model(u, p ,t)
E, x, u_, y = u
τ, α, τ_D, J, U0, ΔU0, τ_y, β, xthr, ythr, I0 = p
U(y, U0, ΔU0, ythr) = U0 + ΔU0 / ( 1 + exp( -50 * ( y - ythr ) ) )
σ(x, xthr)= 1 / (1 + exp(-20 * (x - xthr)));
du1 = (-E + α * log( 1 + exp( ( J * u_ * x * E + I0 ) / α ) )) / τ
du2 = ( 1 - x ) / τ_D - u_ * x * E
du3 = (U(y, U0, ΔU0, ythr) - u_) / τ_F + U(y, U0, ΔU0, ythr) * ( 1 - u_ ) * E
du4 = -y / τ_y + β * σ(x, xthr)
return SVector(du1, du2, du3, du4)
end;
τ = 0.013; τ_D = 0.15; τ_y = 1.8; τ_F = 1;
α = 1.5; J = 3.07; β = 0.4375
ΔU0 = 0.305
xthr = 0.9; ythr = 0.5
parametres = SA[ τ, α, τ_D, J, NaN, ΔU0, τ_y, β, xthr, ythr, NaN ]
timefinal = 500.0
timefinal = 1000
parametres = SA[ τ, α, τ_D, J, 0.245, ΔU0, τ_y, β, xthr, ythr, -1.54 ]
ds = ContinuousDynamicalSystem( model, SA[3.17341815116179, 0.8060004204879812, 0.7442741573700415, 0.03527508347294078],
parametres )
λλ = lyapunovspectrum( ds, timefinal, Ttr = timefinal, Δt = 1;
diffeq = ( alg = RK4(), adaptive = false, dense = false, dt = 0.001 ))
```

Output

4-element Vector{Float64}:

0.0015144553599221596

-0.30907642384764217

-4.779021313105849

-17.721494569637557