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function R = qr_givens (A)
%QR_GIVENS Givens-rotation QR factorization.
% Example:
% R = qr_givens (A)
% See also: cs_demo
% Copyright 2006-2007, Timothy A. Davis.
% http://www.cise.ufl.edu/research/sparse
[m n] = size (A) ;
parent = cs_etree (sparse (A), 'col') ;
A = full (A) ;
for i = 2:m
k = min (find (A (i,:))) ; %#ok
if (isempty (k))
continue ;
end
while (k > 0 & k <= min (i-1,n)) %#ok
A ([k i],k:n) = givens2 (A(k,k), A(i,k)) * A ([k i],k:n) ;
A (i,k) = 0 ;
k = parent (k) ;
end
end
R = sparse (A) ;
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