fun matrix(n,m,v:real) =
         let
             val M = Array.array(n,Array.array(m,v));
             val i = ref 1
         in
             (
                 while !i<n do (
                     Array.update(M,!i,Array.array(m,v));
                     i := !i + 1
                 );
                 M
             )
         end;