title: MATLAB Nyquist Plot - Show the unit circle
body: <p>I cannot find out how you would show the unit circle centered at -1 on a Nyquist plot. </p>
  
  <p>When I plot <code>nyquist(L)</code> with <code>L(s) = P(s)*C(s)</code> being my loop function, it only shows the nyquist plot itself. Using <code>grid on</code> also doesn't do this.</p>
  
  <p>Can someone help me please?</p>