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function est = norm1est (L,U,P,Q)
%NORM1EST 1-norm estimate.
% Example:
% est = norm1est (L,U,P,Q)
% See also: cs_demo
% Copyright 2006-2007, Timothy A. Davis.
% http://www.cise.ufl.edu/research/sparse
n = size (L,1) ;
for k = 1:5
if (k == 1)
est = 0 ;
x = ones (n,1) / n ;
jold = -1 ;
else
j = min (find (abs (x) == norm (x,inf))) ; %#ok
if (j == jold)
break
end ;
x = zeros (n,1) ;
x (j) = 1 ;
jold = j ;
end
x = Q * (U \ (L \ (P*x))) ;
est_old = est ;
est = norm (x,1) ;
if (k > 1 & est <= est_old) %#ok
break
end ;
s = ones (n,1) ;
s (find (x < 0)) = -1 ; %#ok
x = P' * (L' \ (U' \ (Q'*s))) ;
end
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