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## Copyright (C) 1996 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, write to the Free
## Software Foundation, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.
## usage: cond (A)
##
## Return the condition number of A, computed using the singular values
## of A. If the maximum and minimum singular values of A are both zero,
## cond returns Inf rather than NaN.
##
## See also: norm, svd, rank
## Author: jwe
function retval = cond (a)
if (nargin == 1)
[nr, nc] = size (a);
if (nr == 0 && nc == 0)
if (! propagate_empty_matrices)
error ("cond: empty matrix is invalid as argument");
endif
if (strcmp (propagate_empty_matrices, "warn"))
warning ("cond: argument is empty matrix\n");
endif
retval = 0.0;
endif
if (any (any (isinf (a) | isnan (a))))
error ("cond: argument must not contain Inf or NaN values");
else
sigma = svd (a);
sigma_1 = sigma(1);
sigma_n = sigma(length (sigma));
if (sigma_1 == 0 || sigma_n == 0)
retval = Inf;
else
retval = sigma_1 / sigma_n;
endif
endif
else
usage ("cond (a)");
endif
endfunction
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