Normally, a figure window can be maximized by obtaining the underlying Java Frame object and calling its setMaximized
method:
jf = get(handle(gcf), 'JavaFrame');
jf.setMaximized(true)
If this doesn't work, the likely reason is that resizing is disabled for that figure window. You should be able to re-enable resizing this way:
set(gcf, 'Resize', 'on')
Of course, replace gcf
with the handle of the respective figure if it is not the current figure.