function [L, U, ierr] = lunaive(A);
%
% compute a "naive" LU factorization of A (that is, no pivoting)
%
% calling sequence: [L, U, err] = lunaive(A);
%
% A = square input matrix
% L = unit lower triangular factor
% U = upper triangular factor
% 
% output:
%  ierr = 0 - normal termination
%  ierr =-1 - A not square
%  ierr = i>0 - small diagonal encountered at (i,i) position
%