f=@(x,y,z) 2*x+y+z;
x=linspace(0,6,21);
y=linspace(-3,3,20);
z=linspace(-3,3,20);
[X,Y,Z] = meshgrid(x,y,z);
clf
isosurface(X,Y,Z,f(X,Y,Z),4)
colormap copper
g=@(x,y,z) x.^2+y.^2+z.^2-6*x+5;
[X,Y,Z] = meshgrid(x,y,z);
isosurface(X,Y,Z,g(X,Y,Z),0)
axis equal 
%alpha(0.3)
grid
colormap(cool)
%colormap('default') 