This question is about pronunciation of variables with a subindex such as $P_i$.
In this Stanford video lecture on statistical mechanics $P_i$ is pronounced " Pees of i" and $E_i$ is pronounced "Ees of i". Is this pronunciation standard in the US? In Europe I have just heard "Pee i" and "E i".
Most of my lecturers say "P of i" and that's how I say it as well. But I've heard "P sub i" many times.