title: Adding markers on specific points in bodeplot
body: <p>I am currently designing a 5th order Butterworth filter and looking at its transfer function response in Matlab. I have successfully calculated it and have plotted its bode response like this:</p>
  
  <pre><code>% Butterworth Fifth Order Low Pass
  figure(1)
  h = bodeplot(FinalTF);
  setoptions(h,'FreqUnits','Hz','PhaseVisible','off');
  title('Butterworth LowPass Fifth Order');
  grid on;
  </code></pre>
  
  <p>where FinalTF is the transfer function I'm talking about. What I want is to add markers on specific points in this plot (specifically I want to highlight the frequencies fp,fo,fs, you don't need to know what these are, they're just 3 different points on the x-axis, and the dB at each frequency) with code. I know how to do it by clicking on the graph, but that will be too time consuming, as I have many plots to go through. I am currently running into two basic problems:</p>
  
  <p>1) I don't know how to get the specific dB at each frequency just by using the TF object. I tried using the function <a href="http://www.mathworks.com/help/control/ref/evalfr.html" rel="nofollow">evalfr()</a>, but tbh the values it returns seem a bit off.</p>
  
  <p>2) Ignoring the previous point, even if I do the calculations by hand, I <strong>can't</strong> add them on the plot using <a href="http://www.mathworks.com/help/matlab/creating_plots/display-markers-at-specific-data-points-on-line-plot.html" rel="nofollow">this method</a>, and I'm not sure what the problem is. Maybe because I'm using bodeplot instead of regular plot? I don't know how else to do it though.</p>
  
  <p>I'm using Matlab 2015, if it makes any difference.</p>
  
  <p>Any help would be appreciated. Thanks in advance.</p>