$$
\left[\begin{array}{l}
m\frac{{{d^2}x}}{{d{t^2}}} = T\left( t \right)\frac{{x\left( t \right)}}{r}\\
m\frac{{{d^2}y}}{{d{t^2}}} = T\left( t \right)\frac{{y\left( t \right)}}{r} - mg\\
x{\left( t \right)^2} + y{\left( t \right)^2} = {r^2}
\end{array}\right]
$$
Each diagonal element $G_{i,t}^r$ is specified as a logistic cumulative density functions, i.e.
$$
G_{i,t}^r(s_{i,t}^r; γ_i^r, c_i^r) = ≤ft[1 + \exp\big\{-γ_i^r(s_{i,t}^r-c_i^r)\big\}\right]^{-1}
$$
for $i = 1,2, …, \tilde{n}$ and $r=0,1,…,m-1$, so that the first model is a Vector Logistic Smooth Transition AutoRegressive (VLSTAR) model. The ML estimator of θ is obtained by solving the optimization problem
$$
\hat{θ}_{ML} = arg \max_{θ}log L(θ)
$$
where log $L(θ)$ is the log-likelihood function of VLSTAR model, given by
$$
ll(y_t|I_t;θ)=-\frac{T\tilde{n}}{2}\ln(2π)-\frac{T}{2}\ln|Ω|-\frac{1}{2}∑_{t=1}^{T}(y_t-\tilde{G}_tB\,z_t)'Ω^{-1}(y_t-\tilde{G}_tB\,z_t)
$$
The NLS estimators of the VLSTAR model are obtained by solving the optimization problem
$$
\hat{θ}_{NLS} = arg \min_{θ}∑_{t=1}^{T}(y_t - Ψ_t'B'x_t)'(y_t - Ψ_t'B'x_t).
$$
Given some regularity conditions, the GMM estimator converges as $n$ goes to infinity to the following distribution:
$$
\left[
\sqrt{n}(\hat{\theta}-\theta_0) \stackrel{L}{\rightarrow} N(0,V),
\right]
$$
where
$$
\left[
V = E\left(\frac{\partial g(\theta_0,x_i)}{\partial\theta}\right)'\Omega(\theta_0)^{-1}E\left(\frac{\partial g(\theta_0,x_i)}{\partial\theta}\right)
\right]
$$
Inference can therefore be performed on $\hat{\theta}$ using the assumption that it is approximately distributed as $N(\theta_0,\hat{V}/n)$.