平方和

syms x y;
r2 = x^2+y^2;
fsurf(r2,[-30 30],'ShowContours','on')

或者

r2 = @(x,y)(x.^2+y.^2);
fsurf(r2,[-30 30],'ShowContours','on')

墨西哥草帽

syms x y;
r2=x^2+y^2;
r=sqrt(r2)+eps;
z=sin(r)./r;
fsurf(z,[-10 10],'ShowContours','on');