fix_x_limits fixes all axis in current figure to the maximum span found
fix_x_limits(h) fixes XLim property of all axis objects in h or all axes parented under h if figure handles to maximum span found within all axes
fix_x_limits(h,limits) fixes all to given limits: [minx maxx]

Example:
h1 = subplot(2,1,1);hist(rand(100,1));
h2 = subplot(2,1,2);hist(randn(100,1));
fix_x_limits % set the maximum limits to all axes in current figure
fix_x_limits([h1 h2],[-3 3]) % Give the limits to the axis objects
fix_x_limits(gcf,[-5 4]) % Give the limits to the figure object