function rd()
y=[linspace(0,0,800);linspace(1,1,800)];
x=[linspace(3,6,800);linspace(3,6,800)];
z=[5*sind(linspace(90,0,800));5*sind(linspace(90,0,800))];
mesh(x,y,7.5-z);
hold on
z=[6*sind(linspace(90,0,800));6*sind(linspace(90,0,800))];
mesh(x,y,7.5-z);
hold on
z=[1.5+5*sind(linspace(90,0,800));1.5+5*sind(linspace(90,0,800))];
mesh(x,y,7.5-z);
hold on
z=[1.5+6*sind(linspace(90,0,800));1.5+6*sind(linspace(90,0,800))];
mesh(x,y,7.5-z);
hold on