xvec=linspace(0,1,50);
yvec=linspace(-1,1,50);
zvec=yvec;
[X,Y,Z]=meshgrid(xvec,yvec,zvec);
R=(X.*X+Y.*Y+Z.*Z).^(0.5);
cosmat=cos(2*pi*R*2);
indx= find(R>0.99);
cosmat(indx)=NaN*ones(1,length(indx));
figure;p=patch(isosurface(X,Y,Z,cosmat,0));
isonormals(X,Y,Z,cosmat,p)
set(p,'FaceColor','red','EdgeColor','none');
daspect([1 1 1])
view(3)
camlight
lighting phong