Question

I am using plotyy to plot two vectors on different y-axes. I wish to add a third vector to one of the two axes. Can someone please tell me why the following code is not working?

[ax h1 h2] = plotyy(1:10,10*rand(1,10),1:10,rand(1,10));
hold on; plot(ax(2),1:10,rand(1,10));
??? Error using ==> plot
Parent destroyed during line creation

I simply wish to add an additional vector to one of the axes (ax(1),ax(2)) created by plotyy.

Answer 1

Apply hold to the axis of interest.

[ax h1 h2] = plotyy(1:10,10*rand(1,10),1:10,rand(1,10));
hold(ax(2), 'on'); 
plot(ax(2),1:10,rand(1,10));

plotyy works by creating two axes, one on top of the other. You are carefully adding the new vector to the second axis. The hold property is also a per-axis property, so you just need to make sure that the hold is set on the same axis.