Cannot add line to magnitude graph after FFT

I tried to use FFT to transfer a time domain data to frequency domain, and it appear two graphs (magnitude against frequency and phrase against frequency). I want to hide phrase graph and add a vertical line to the magnitude graph. However, the line only add to the phrase graph even I have hidden it. Could any talented matlab user advise how can I add the vertical line to the magnitude graph? Thank you!

T = 0.001

G3data1 = iddata(G3x1,[],T)
G3data2 = iddata(G3x2,[],T)
G3data3 = iddata(G3x3,[],T)
G3data4 = iddata(G3x4,[],T)

M3f1 = fft(G3data1)
M3f2 = fft(G3data2)
M3f3 = fft(G3data3)
M3f4 = fft(G3data4)

M3f = merge(M3f1, M3f2, M3f3, M3f4,N)

opt = dataPlotOptions('frequency');
opt.PhaseVisible = 'off'; 
opt.Xlim =  [1 50];
opt.FreqUnits = 'Hz';
opt.FreqScale = 'linear';

plot(M3f,opt)
xline(5)
title('Frequency Graph')
legend({'data1','data2','data3','data4'})

Answer 1

[Shivansh]

Hi Sam,

You can add a vertical line to the magnitude graph while hiding the phase graph by adding the line to the correct axes.

You can refer to the following code snippet for reference:

% Plot the data with phase hidden
plot(M3f, opt);

% Get handles to the axes
ax = gca; % Get current axes, assuming it's the magnitude plot

% Add a vertical line to the magnitude plot
xline(ax, 5);

% Customize the plot
title(ax, 'Frequency Graph');
legend(ax, {'data1', 'data2', 'data3', 'data4'});

I hope this resolves the issue!