How to indicate a specific mad and phase value on bode plot given the freq in Matlab?

Question

What I want to to is plot the bode plot of a transfer function

sys = tf([1],[1,1]);

then call

bode(sys);

but I also want to input particular frequencies where the bode plot marks the freq and display the value of mag and phase at that point.

So basically like a data point on the bode plot at the freq I input.

for example once I call bode(sys); the plot shows the (mag,freq) & (mag, phase) values at 2Khz, 120KHz etc

I would really aprreciate some help.

Thanks

Answer 1

There are 2 things I can think of. Both require you to calculate the value of the magnitude and phase for those particular frequency values and store them in arrays: Frequency, Magnitude, Phase.

Approach 1) Download this script: http://www.mathworks.in/matlabcentral/fileexchange/9973-gridxy-v2-2-feb-2008

and try this:

   bodemag(sys);
   hold on;
   gridxy(Frequency, Magnitude);

Approach 2)

   bodemag(sys);
   hold on;
   text(Frequency, Magnitude, num2str(Magnitude));

I dont know how to reference the phase plot. If you are able to reference the phase plot, then you should be able to do the same for that plot too. This link has some suggestions for phase only plot in matlab: http://www.mathworks.in/matlabcentral/newsreader/view_thread/247644