# Inserting vertical and horizontal line in bodeplot

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Carl Overgaard on 30 Nov 2019
Commented: Carl Overgaard on 30 Nov 2019
Hello
With below code I have made a bode plot. Then I have calculatted an angular frequency.
I want to insert a vertical line from my found angular frequency(found to be 0.041889), and also a horizontal line so I can determine the phase angel on the y-axis:
Can this be done?
IThe plan is that it should look like this:
My code:
sys1=tf([1805.1],[4637.61 136.2 1]) %transfer function
w=logspace(-5,2); %Define frequency range
[A,phi]=bode(sys1,w); %Amplitude ratio (A) and phase shift (phi)
figure
subplot(2,1,1)
loglog(w,A(:)) %Amplitude ratio vs frequency
grid on
ylabel('AR')
subplot(2,1,2)
semilogx(w,phi(:))
ylabel('Phase angle(Degrees)')
legend({'Lower tank'},'Fontsize',14) %add "title" to plot...

Stephan on 30 Nov 2019
Edited: Stephan on 30 Nov 2019
xline and yline should work for this purpose. Both functions were introduced with R2018b. If you use an earlier release, just define two points for every line you need and use the plot command combined with hold on and hold off including the line format as you wish it to look like.

Carl Overgaard on 30 Nov 2019
The x-line makes sense(that´s the 0.041889) but how do I make the y-line that intersect the x-line and the bode plot in my code?
Stephan on 30 Nov 2019
you could interpolate:
phi1 = squeeze(phi);
ypoint = interp1(w,phi1,0.041889)
ypoint =
-140.6024
the whole code would look like:
sys1=tf([1805.1],[4637.61 136.2 1]) %transfer function
w=logspace(-5,2); %Define frequency range
[A,phi]=bode(sys1,w); %Amplitude ratio (A) and phase shift (phi)
figure
subplot(2,1,1)
loglog(w,A(:)) %Amplitude ratio vs frequency
grid on
ylabel('AR')
subplot(2,1,2)
semilogx(w,phi(:))
ylabel('Phase angle(Degrees)')
legend({'Lower tank'},'Fontsize',14) %add "title" to plot...
hold on
phi1 = squeeze(phi);
ypoint = interp1(w,phi1,0.041889)
scatter(0.041889,ypoint,'or')
xline(0.041889,'--r')
yline(ypoint,'--r')
Carl Overgaard on 30 Nov 2019
Thank you!!