$$ \begin{equation} \begin{aligned} \frac{dx}{dt} &= \alpha (y(t) - h) \\[5pt] \frac{dy}{dt} &= x(t) - y(t) + z(t) \\[5pt] \frac{dz}{dt} &= - \beta y(t) \\[10pt] h &= -b \sin(\frac{\pi x(t)}{2a}) + d \\ \end{aligned} \end{equation} $$