Peak Value from bodemag plot

I am trying to calculate the peak value of the bodemag plot. Attached is the code I am trying to use

[gpeak,fpeak] = getPeakGain(SS_1)
gpeak_dB = 20*log10(gpeak);

However that doesn't seem to work for bodemag plots, only for bode plots because it isn't giving me the correct peak for the plot attached.

How do I calculate the peak of a bodemag plot?

Answer 1

[Star Strider]

Try this:

F = openfig('untitled.fig');
getF = get(F);
Lines = findobj(F, 'Type','Line');

for k = 1:numel(Lines)
    X{k} = Lines(k).XData;
    Y{k} = Lines(k).YData;
    [Ymax,Idx] = max(Y{k});
    FM{k,:} = [X{k}(Idx) Ymax  Idx];
end
MagFreq = array2table(cell2mat(FM), 'VariableNames',{'Frequency','Magnitude','Index'})

producing:

MagFreq =

    Frequency     Magnitude     Index
    _________    ___________    _____

        NaN              NaN      1  
        NaN              NaN      1  
      1e-20       1.2722e-14      1  
      1e-20                0      1  
      1e-20       1.2722e-14      1  
      1e-20       2.5444e-14      1  
      1e-20                0      1  
      1e-20       1.7358e-14      1  
     1.6051          0.52101     35  
      1e-20      -2.5073e-14      1  
     1.3159         0.062431     32  
      1e-20      -2.5073e-14      1

It is not difficult to extract the values, however it is definitely not straightforward.

[JD]

Hi Star Strider,

Thanks for the quick response.

If I am looking at the table correctly, i would pick the largest magnitude in the table as the maximum value of the bodemag plot, is that correct?

Thanks

[Star Strider]

My pleasure.

‘If I am looking at the table correctly, i would pick the largest magnitude in the table as the maximum value of the bodemag plot, is that correct?’

It depends on the information you want. There are 12 entries, 10 of them finite. I have no idea what they represent because I only have the figure that plots them.

So, probably yes. The maximum magnitude is 0.52101 dB at 1.6051 rad/s

Note that the values are in dB because they are plotted in dB. No conversion to dB is necessary.

[JD]

That makes a lot of sense! Thank you so much for your input and help!

[Star Strider]

As always, my pleasure!