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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: tril (x, k)
##
## Return the lower triangular part of x above the k-th diagonal. If
## the second argument is omitted, k = 0 is assumed.
##
## See also: triu, diag
## Author: jwe
function retval = tril (x, k)
if (nargin > 0)
[nr, nc] = size (x);
retval = zeros (nr, nc);
endif
if (nargin == 1)
k = 0;
elseif (nargin == 2)
if ((k > 0 && k > nc) || (k < 0 && k < -nr))
error ("tril: requested diagonal out of range");
endif
else
usage ("tril (x [, k])");
endif
for j = 1 : min (nc, nr+k)
nr_limit = max (1, j-k);
retval (nr_limit:nr, j) = x (nr_limit:nr, j);
endfor
endfunction
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