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−## Copyright (C) 1996, 1997 John W. Eaton
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−##
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−## This file is part of Octave.
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−##
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−## Octave is free software; you can redistribute it and/or modify it
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−## under the terms of the GNU General Public License as published by
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−## the Free Software Foundation; either version 2, or (at your option)
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−## any later version.
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−##
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−## Octave is distributed in the hope that it will be useful, but
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−## WITHOUT ANY WARRANTY; without even the implied warranty of
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−## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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−## General Public License for more details.
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−##
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−## You should have received a copy of the GNU General Public License
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−## along with Octave; see the file COPYING.  If not, write to the Free
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−## Software Foundation, 59 Temple Place - Suite 330, Boston, MA
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−## 02111-1307, USA.
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−
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−## -*- texinfo -*-
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−## @deftypefn {Function File} {} polyderiv (@var{c})
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−## @deftypefnx {Function File} {[@var{q}] =} polyder (@var{b}, @var{a})
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−## @deftypefnx {Function File} {[@var{q}, @var{r}] =} polyder (@var{b}, @var{a})
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−## Return the coefficients of the derivative of the polynomial whose
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−## coefficients are given by vector @var{c}.  If a pair of polynomials
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−## is given @var{b} and @var{a}, the derivative of the product is
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−## returned in @var{q}, or the quotient numerator in @var{q} and the
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−## quotient denominator in @var{r}.
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−## @end deftypefn
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−## @seealso{poly, polyinteg, polyreduce, roots, conv, deconv, residue,
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−## filter, polygcd, polyval, and polyvalm}
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−
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−## Author: Tony Richardson <arichard@stark.cc.oh.us>
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−## Created: June 1994
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−## Adapted-By: jwe
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−
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−function [q, r] = polyderiv (p, a)
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−
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−  if (nargin == 1 || nargin == 2)
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−    if (! isvector (p))
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−      error ("polyderiv: argument must be a vector");
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−    endif
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−    if (nargin == 2)
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−      if (! isvector (a))
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−	error ("polyderiv: argument must be a vector");
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−      endif
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−      if (nargout == 1) 
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−	## derivative of p*a returns a single polynomial
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−	q = polyderiv (conv (p, a));
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−      else
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−	## derivative of p/a returns numerator and denominator
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−	r = conv (a, a);
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−	if (numel (p) == 1)
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−	  q = -p * polyderiv (a);
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−	elseif (numel (a) == 1)
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−	  q = a * polyderiv (p);
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−	else
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−	  q = conv (polyderiv (p), a) - conv (p, polyderiv (a));
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−	  q = polyreduce (q);
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−	endif
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−
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−	## remove common factors from numerator and denominator
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−	x = polygcd (q, r);
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−	if (length(x) != 1)
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−	  q = deconv (q, x);
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−	  r = deconv (r, x);
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−	endif
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−
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−	## move all the gain into the numerator
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−	q = q/r(1);
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−	r = r/r(1);
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−      endif
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−    else
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−      lp = numel (p);
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−      if (lp == 1)
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−	q = 0;
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−	return;
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−      elseif (lp == 0)
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−	q = [];
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−	return;
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−      endif
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−
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−      ## Force P to be a row vector.
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−      p = p(:).';
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−
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−      q = p(1:(lp-1)) .* [(lp-1):-1:1];
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−    endif
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−  else
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−    usage ("q = polyderiv (p) or q = polyderiv (b, a) or [q, r] = polyderiv (b, a)");
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−  endif
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−
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−
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−endfunction