How do I make this function work for any matrix size?

%How do I change this function so that it works for matrices of any size?

function [B] = Matrices(matrice)

B = matrice;
B(1,1) = 0;
B(1,2) = 0;
B(1,3) = 0;
B(2,2) = 0;
B(2,3) = 0;
B(3,3) = 0;
end

%So that calling this
[B] = Matrices([1 2 3; 4 5 6; 7 8 9])
%Will return
B =

     0     0     0
     4     0     0
     7     8     0

Answer 1

[Walter Roberson]

function B = Matrices(matrice)
   B = tril(matrice,-1);
end