Vertical refline in matlab?

Question

How do I draw a vertical refline in matlab? e.g. I want to plot a line of x=5. Obviously using inf does not help at all. Can anyone give some advice?

Answer 1

There is an excellent answer over on https://stackoverflow.com/a/8108766/1194420 repeated below for convenience. (Please go there an up vote the original answer) ---

There exist an undocumented function graph2d.constantline:

plot(-2:5, (-2:5).^2-1)
%# vertical line
hx = graph2d.constantline(0, 'LineStyle',':', 'Color',[.7 .7 .7]);
changedependvar(hx,'x');
%# horizontal line
hy = graph2d.constantline(0, 'Color',[.7 .7 .7]);
changedependvar(hy,'y');