working with matrices

hello

i want to fill a matrix by its upper off diagonal elements

specifically I want to take the first and second column of? the matrix and I apply a function to then that returns a single number which I want to place in the (1,2) entry of the matrix, then I want to take the first and third column of the matrix and apply the same function, get the single number and place it to (2,3) entry of the matrix and so on

how can i do it?

thanks
anna