pdetool change axes limits

How to change the x and y axes limits in pdetool by coding in an .m file. the code snippet in help file doesn't seem to work.

set(ax,'XLim',[-10 10]);  
set(ax,'YLim',[-10 10]);  
set(ax,'XTickMode','auto');  
set(ax,'YTickMode','auto');

what should be added before/after this for setting the limits. thanks.