//Generate (useless) data
x=0:1:10;  // size: 1*11
y=0:1:100; // size: 1*101
z=x'*y;    // size: 11*101
z2=z/2;

//Plot
scf(); //Create a new grahic window
xset("colormap",jetcolormap(64)); // Choose colormap (see the help of colormap)

//First subplot
subplot(2,1,1);
xtitle("Big Data", "x coordinate", "y coordinate");
colorbar(min(z),max(z));
Sgrayplot(x, y, z, zminmax = [min(z) max(z)]);

//Second subplot with the same scale
subplot(2,1,2);
xtitle("Small Data", "x coordinate", "y coordinate");
colorbar(min(z),max(z)); // Same colorbar
Sgrayplot(x, y, z2, zminmax = [min(z) max(z)]); // Note that zminmax is the same!