Anyway, let's find the transition matrix P...
The adjacent corners to 1 are 4 and 2
The ac to 2 are 1 & 3
The ac to 3 are 2 & 4
The ac to 4 are 3 & 1
So we have
Just find such that
This is just a simple matrix multiplication.
If I misunderstood what you don't understand, just tell me, I'll try to help as much as possible...