### view scripts/polynomial/polyder.m @ 15489:481417a57a2d

improve sign and signbit docs * mappers.cc (Fsign): Note sign (-0) is 0. Add @seealso for signbit. (Fsignbit): Add @seealso for sign.
author John W. Eaton Thu, 04 Oct 2012 10:20:59 -0400 5d3a684236b0
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```
## Copyright (C) 1994-2012 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## the Free Software Foundation; either version 3 of the License, 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, see

## -*- texinfo -*-
## @deftypefn  {Function File} {} polyder (@var{p})
## @deftypefnx {Function File} {[@var{k}] =} polyder (@var{a}, @var{b})
## @deftypefnx {Function File} {[@var{q}, @var{d}] =} polyder (@var{b}, @var{a})
## Return the coefficients of the derivative of the polynomial whose
## coefficients are given by the vector @var{p}.  If a pair of polynomials
## is given, return the derivative of the product @math{@var{a}*@var{b}}.
## If two inputs and two outputs are given, return the derivative of the
## polynomial quotient @math{@var{b}/@var{a}}.  The quotient numerator is
## in @var{q} and the denominator in @var{d}.
## @seealso{polyint, polyval, polyreduce}
## @end deftypefn

## Author: Tony Richardson <arichard@stark.cc.oh.us>
## Created: June 1994

function [q, d] = polyder (p, a)

if (nargin == 1 || nargin == 2)
if (! isvector (p))
error ("polyder: argument must be a vector");
endif
if (nargin == 2)
if (! isvector (a))
error ("polyder: argument must be a vector");
endif
if (nargout == 1)
## derivative of p*a returns a single polynomial
q = polyder (conv (p, a));
else
## derivative of p/a returns numerator and denominator
d = conv (a, a);
if (numel (p) == 1)
q = -p * polyder (a);
elseif (numel (a) == 1)
q = a * polyder (p);
else
q = conv (polyder (p), a) - conv (p, polyder (a));
q = polyreduce (q);
endif

## remove common factors from numerator and denominator
x = polygcd (q, d);
if (length (x) != 1)
q = deconv (q, x);
d = deconv (d, x);
endif

## move all the gain into the numerator
q = q/d(1);
d = d/d(1);
endif
else
lp = numel (p);
if (lp == 1)
q = 0;
return;
elseif (lp == 0)
q = [];
return;
endif

## Force P to be a row vector.
p = p(:).';

q = p(1:(lp-1)) .* [(lp-1):-1:1];
endif
else
print_usage ();
endif

endfunction

%!assert (polyder ([1, 2, 3], [2, 2]))
%!assert (polyder (13), 0)

%!error polyder ([])
%!error polyder (1,2,3)
%!error <argument must be a vector> polyder ([1, 2; 3, 4])

```