Book 1 Section 11.2 Formula Missing a Variable

[ReneeeZhang]

The highlighted formula in the following screenshot is missing a variable

$$ \mathbf{R}'\perp = \frac{\eta}{\eta'} \left( \mathbf{R} + \cos \theta \mathbf{n} \right)$$ is wrong.
It should be:
$$ \mathbf{R}'\perp = \frac{\eta}{\eta'} \left( \mathbf{R} + |\mathbf{R}|\cos \theta \mathbf{n} \right) $$
Looks like:

[hollasch]

Note that in our code, $\mathbf{R}$ is a unit vector.

[ReneeeZhang]

Thank you. I do notice that in the code $\mathbf{R}$ is a unit vector, but in the book, it does not explicitly say this assumption, which was a bit confusing when I tried to reason about the formula myself.

[hollasch]

Yeah, I noticed the same thing while going through the equations to verify. Your suggestion is a good one.