How Mathematics formula makes

How Mathematics formula makes a ball

X = 2*rand(n,3)-1;
v = sum(X.^2,2);
>> delta = 0.05;
d = -1:delta:1;
[x0,y0,z0] = meshgrid(d,d,d);
X0 = [x0(:), y0(:), z0(:)];
v0 = griddatan(X,v,X0);
v0 = reshape(v0, size(x0));
>> p = patch(isosurface(x0,y0,z0,v0,0.6));
isonormals(x0,y0,z0,v0,p);
set(p,'FaceColor','red','EdgeColor','none');
view(3);
camlight;
lighting phong
axis equal
title('Interpolated sphere from scattered data')