===== Primitive: Sphere (ball) =====
**Definition**: <m>R^2-(x-x_0)^2-(y-y_0)^2-(z-z_0)^2</m>

**Call**: hfSphere(x,center,R);

**Parameters**:

x - point coordinates array

center - sphere center array

R - sphere radius

**Test file**: [[http://hyperfun.org/sphere.hf|sphere.hf]]