Hello Bryce,
As per my understanding, you are trying to plot a horizontal line, on an already generated wcoherence plot.
To retain the current plot in MATLAB, we have to use the "hold on" function. "hold on" retains plots in the current axes so that new plots added to the axes do not delete existing plots. For your case the script would look like:
figure;
rng default;
t = 0:0.001:2;
x = cos(2*pi*10*t).*(t>=0.5 & t<1.1)+ ...
cos(2*pi*50*t).*(t>= 0.2 & t< 1.4)+0.25*randn(size(t));
y = sin(2*pi*10*t).*(t>=0.6 & t<1.2)+...
sin(2*pi*50*t).*(t>= 0.4 & t<1.6)+ 0.35*randn(size(t));
wcoherence(x,y,seconds(0.001));
% Hold the previous plot to generate the next plots over it
hold on
linex = [min(t) max(t)];
liney = [0.2 0.2];
plot (linex, log2(liney), 'w-', 'linewidth', 1);
text (min(t)+0.1, log2(0.2+0.05), '0.2 seconds');
You can refer to the following documentation on "hold" for more information:
