Task

Find and display the sum of elements that are below the main diagonal of a matrix.

The matrix should be a square matrix.



 ───   Matrix to be used:   ───


     [[1,3,7,8,10],
      [2,4,16,14,4],
      [3,1,9,18,11],
      [12,14,17,18,20],
      [7,1,3,9,5]] 



 
// Sum below leading diagnal. Nigel Galloway: July 21st., 2021
let _,n=[[ 1; 3; 7; 8;10];
         [ 2; 4;16;14; 4];
         [ 3; 1; 9;18;11];
         [12;14;17;18;20];
         [ 7; 1; 3; 9; 5]]|>List.fold(fun(n,g) i->let i,_=i|>List.splitAt n in (n+1,g+(i|>List.sum)))(0,0) in printfn "%d" n
 