In this module we have developed the dynamic modeling equations
for a perfectly mixed stirred tank heater. We solved for the
steady-state conditions, linearized to obtain the state space
model, and found the transfer function model. We compared the
step responses of the linear and nonlinear models. We also showed
the importance of the ``direction'' of initial conditions. Perturbations
in certain directions cause a fast response, while perturbations
in other directions yield a slow response.