function calcRationalCurveDerivatives( Pders ) {

	const nd = Pders.length;
	const Aders = [];
	const wders = [];

	for ( let i = 0; i < nd; ++ i ) {

		const point = Pders[ i ];
		Aders[ i ] = new Vector3( point.x, point.y, point.z );
		wders[ i ] = point.w;

	}

	const CK = [];

	for ( let k = 0; k < nd; ++ k ) {

		const v = Aders[ k ].clone();

		for ( let i = 1; i <= k; ++ i ) {

			v.sub( CK[ k - i ].clone().multiplyScalar( calcKoverI( k, i ) * wders[ i ] ) );

		}

		CK[ k ] = v.divideScalar( wders[ 0 ] );

	}

	return CK;

}
Calculates derivatives (0-nd) of rational curve. See The NURBS Book, page 127, algorithm A4.2.

@param {Array<Vector4>} Pders - Array with derivatives.
@return {Array<Vector3>} An array with derivatives for rational curve.