If P has 1’s on the antidiagonal from (1, n) to (n, 1), describe PAP. Note P = {P}^{T}.
If P has 1’s on the antidiagonal from (1, n) to (n, 1), describe PAP. Note P = {P}^{T}.
The “reverse identity” P takes (1, …, n) into (n, …, 1).
When rows and also columns are reversed, (PAP)_{ij} is (A)_{n-i+1,n-j+1}.
In particular (PAP)_{11} is {A}_{nn}.