# Copyright (C) 1995 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, 675 Mass Ave, Cambridge, MA 02139, USA.

function p = polyderiv (p)

# usage: polyderiv (p)
#
# Returns the coefficients of the derivative of the polynomial whose
# coefficients are given by vector p.
#
# SEE ALSO: poly, polyinteg, polyreduce, roots, conv, deconv, residue,
#           filter, polyval, polyvalm

# Written by Tony Richardson (amr@mpl.ucsd.edu) June 1994.

  if (nargin != 1)
    usage ("polyderiv (vector)");
  endif

  if (is_matrix (p))
    error ("argument must be a vector");
  endif

  lp = length (p);
  if (lp == 1)
    p = 0;
    return;
  elseif (lp == 0)
    p = [];
    return;
  end

  p = p (1:(lp-1)) .* [(lp-1):-1:1];

endfunction