Create sphere

`[X,Y,Z] = sphere`

returns the *x*-,
*y*-, and *z*- coordinates of a sphere
without drawing it. The returned sphere has a radius equal to
`1`

and consists of 20-by-20 faces.

The function returns the *x*-, *y*-, and
*z*- coordinates as three
`21`

-by-`21`

matrices.

To draw the sphere using the returned coordinates, use the
`surf`

or `mesh`

functions.