File: cond1est.m

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function c = cond1est (A)   % estimate of 1-norm condition number of A
[m n] = size (A) ;
if (m ~= n || ~isreal (A))
    error ('A must be square and real') ;
end
if isempty(A)
    c = 0 ;
    return ;
end
[L,U,P,Q] = lu (A) ;
if (~isempty (find (abs (diag (U)) == 0)))
    c = Inf ;
else
    c = norm (A,1) * norm1est (L,U,P,Q) ;
end