makeRotationZ( theta ) {

		const c = Math.cos( theta ), s = Math.sin( theta );

		this.set(

			c, - s, 0, 0,
			s, c, 0, 0,
			0, 0, 1, 0,
			0, 0, 0, 1

		);

		return this;

	}
Sets this matrix as a rotational transformation around the Z axis by
the given angle.

@param {number} theta - The rotation in radians.
@return {Matrix4} A reference to this matrix.