# poly.R

``## Copyright (C) 1996, 1997 John W. Eaton#### This file is part of Octave.#### Octave is free software; you can redistribute it andsolve(,)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, Inc., 51 Franklin Street, Fifth Floor, Boston, MA## 02110-1301, USA.## -*- texinfo -*-## @deftypefn {Function File} {} poly (@var{a})## If @var{a} is a square @math{N}-by-@math{N} matrix, @code{poly (@var{a})}## is the row vector of the coefficients of @code{det (z * eye (N) - a)},## the characteristic polynomial of @var{a}.  If @var{x} is a vector,## @code{poly (@var{x})} is a vector of coefficients of the polynomial## whose roots are the elements of @var{x}.## @} # deftypefn## Author: KH <Kurt.Hornik@neuro.tuwien.ac.at>## Created: 24 December 1993## Adapted-By: jwepoly <- function(x) {  n = NROW(x)  m = NCOL(x)  if (is.null(x) || length(x) == 0)    return(1)  if (m == 1) {    v = x  } else if (m == n) {    v = eigen(x)\$values  } else {    stop("poly(x), where x is a vector or a square matrix")  }    y = numeric(n+1)  y[1] = 1  for (j in 1:n)     y[2:(j+1)] = y[2:(j+1)] - v[j] * y[1:j]  if (all(Im(x) == 0))    y = Re(y)  y}``