where is the formula in c++ file

[fatalfeel]

https://github.com/Mikoto10032/DeepLearning/blob/master/books/%5B%E6%B7%B1%E5%BA%A6%E5%BC%BA%E5%8C%96%E5%AD%A6%E4%B9%A0%5D%5BHung-yi%20Lee%5D/PPO%20(v3).pdf

in this pdf page 9. formula as this
𝑝𝜃 𝜏 = 𝑝 𝑠1 𝑝𝜃 𝑎1|𝑠1 𝑝 𝑠2|𝑠1, 𝑎1 𝑝𝜃 𝑎2|𝑠2 𝑝 𝑠3|𝑠2, 𝑎2 ⋯

where is the formula in c++ file? which function implement it? or where define it?
help me find out

[Omegastick]

AFAIK, that formula is a natural consequence of the policy gradient algorithm, and not directly defined anywhere in the code.

[fatalfeel]

In Bayes network its real calculate the conditional probability (http://dlib.net/bayes_net_ex.cpp.html)

PPO algorithm have this formula ex: 𝑝𝜃(𝑎𝑡|𝑠t)
https://github.com/Mikoto10032/DeepLearning/blob/master/books/%5B%E6%B7%B1%E5%BA%A6%E5%BC%BA%E5%8C%96%E5%AD%A6%E4%B9%A0%5D%5BHung-yi%20Lee%5D/PPO%20(v3).pdf

I can not connect the 𝑝𝜃(𝑎𝑡|𝑠t) to source code... or a lot of summation
Y = W x Input + B represent this probability?
I am confused with the formula relate to source code. please help solve it