## 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: triu (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
