How to add a secondary axis to a .fig ?

I know that a secondary axis can be added using e.g. yyaxis and that its properties can then also be edited in the property editor of the figure. However I could not find how to add a secondary axis to a saved .fig, how would one do that ?

Answer 1

[Johannes Hougaard]

Use the function 'open' to load the saved figure to a variable (a handle) and use yyaxis to add the secondary axis

figure;
axes;
x = linspace(-4*pi,4*pi,200);
plot(x,sin(x))

savefig(gcf,'newfigure.fig');
nf = open('newfigure.fig');
yyaxis(nf.CurrentAxes,'right');
plot(x,cos(x./3))