The Simulink® model `watertank` includes the nonlinear Water-Tank System plant and a PI controller in a single-loop feedback system.
 Variables H is the height of water in the tank.Vol is the volume of water in the tank.V is the voltage applied to the pump. Parameters A is the cross-sectional area of the tank.b is a constant related to the flow rate into the tank.a is a constant related to the flow rate out of the tank. Differential equation `$\frac{d}{dt}Vol=A\frac{dH}{dt}=bV-a\sqrt{H}$` States H Inputs V Outputs H