x=-4:0.1:4;y=-4:0.1:4;[X,Y]=meshgrid(x,y);Z=sqrt(X.^2+Y.^2);mesh(X,Y,Z)
x=-10:0.1:10;y=-10:0.1:10;z=sqrt(x.^2+y.^2);plot3(x,y,z)
