Adding a label with text on a plot

I have a plot of some data and I want to highlight one of its distinct peaks like this:

Is there any way that I can do this?

Answer 1

[Chunru]

x = -3:.1:3

x = 1x61

-3.0000 -2.9000 -2.8000 -2.7000 -2.6000 -2.5000 -2.4000 -2.3000 -2.2000 -2.1000 -2.0000 -1.9000 -1.8000 -1.7000 -1.6000 -1.5000 -1.4000 -1.3000 -1.2000 -1.1000 -1.0000 -0.9000 -0.8000 -0.7000 -0.6000 -0.5000 -0.4000 -0.3000 -0.2000 -0.1000

y = exp(-(x-0.5).^2/2);

plot(x, y)
% need to adjust the coordinates (normalized unit)
% doc annotation for more details
annotation("doublearrow", [0.58 0.58], [0.12 0.93]); 

text(0.5, 0.4, "a", "Color", "r")  % data unit