CCD-当中星点位置何计算？

在实验设计当选择RSM =>Central Composite，当中关于星点位置是如何计算的？期望高人给予指点。

以下是Minitab中找到解释：
Alpha for axial points
The distance of each axial point (also called star point) from the center in a central composite design. This value (a), along with the number of center points, determines whether a design can be orthogonally blocked and is rotatable.

举例来说就是：
当因子数为2时，Default Alpha=1.414 (如何计算1.414)

当因子数为3时，1 Block, Default alpha=1.682(如何计算1.682)
2 Block, Default alpha=1.633(如何计算1.633)