function try_lu (A, method, issym)
% sparse LU factorization of A
%
% MATLAB Primer, 6th Edition
% Kermit Sigmon and Timothy A. Davis
% Section 13.4, page 72.

figure (1) 
clf reset
subplot (2, 2, 1) 
spy (A) 
title ('Original matrix A') 
t = cputime ;
if (nargin > 2)
    S = spones (A) + spones (A') ;
    p = feval (method, S) ;
    A = A (p,p) ;
elseif (nargin > 1)
    q = feval (method, A) ;
    A = A (:,q) ;
end
torder = cputime - t
subplot (2, 2, 2) 
spy (A) 
title ('Permuted matrix A') 
t = cputime ;
[L, U, P] = lu (A) ; 
tlu = cputime - t
total = torder + tlu
subplot (2, 2, 3) 
spy (L+U) 
title ('LU factors') 
normest (L*U-P*A) 
Lnz = full (sum (spones (L))) - 1 ; 
Unz = full (sum (spones (U')))' - 1 ; 
flop_count = 2*Lnz*Unz + sum (Lnz) 
subplot (2, 2, 4) 
S = spones (A) ;
etreeplot (S'*S)
title ('column elimination tree')