Start with the total degrees of freedom, which is three times the number of atoms in the molecule.

当运动不受阻碍时，振动种类数量是原子数量的三倍。

That's the total degrees of freedom we had for all of the data combined.

这是我们对所有数据组合的总自由度。

This is equal to mn minus 1 degrees of freedom, which is exactly the total degrees of freedom we had for the total sum of squares.

这等于 mn 减去 1 个自由度，这恰好是总平方和的总自由度。