Here is a doc for two x-axes and y-axes: DOC
Here is how to create two x-axes:
x1=0:.1:2*pi;
Y1 = sin(2*x1);
x2 = -pi:.1:pi;
Y2 = cos(2*x2);
t = tiledlayout(1,1);
ax1 = axes(t);
plot(ax1,x1,Y1,'r-o')
ax1.XColor = 'r';
ax1.YColor = 'r';
ax2 = axes(t);
plot(ax2,x2,Y2,'bd-.')
ax2.XAxisLocation = 'top';
ax2.YAxisLocation = 'right';
ax2.Color = 'none';
ax1.Box = 'off';
ax2.Box = 'off';
ylabel('cos(x_2)')
xlabel('x_2')
grid on
