code: public static double dotProduct4(
      final double x0,
      final double y0,
      final double z0,
      final double w0,
      final double x1,
      final double y1,
      final double z1,
      final double w1)
    {
      final double x = x0 * x1;
      final double y = y0 * y1;
      final double z = z0 * z1;
      final double w = w0 * w1;
      return x + y + z + w;
    }
docs: Calculate the dot product of
  {@code (x0, y0, z0, w0)} and {@code (x1, y1, z1, w1)}.
  
  @param x0 The X component of the first vector
  @param y0 The Y component of the first vector
  @param z0 The Z component of the first vector
  @param w0 The W component of the first vector
  @param x1 The X component of the second vector
  @param y1 The Y component of the second vector
  @param z1 The Z component of the second vector
  @param w1 The W component of the second vector
  
  @return The dot product