--- /dev/null
+## Copyright (C) 2009 Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope 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 3 of the License, or
+## (at your option) any later version.
+##
+## LTI Syncope 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 LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{str} =} tfpoly2str (@var{p})
+## @deftypefnx {Function File} {@var{str} =} tfpoly2str (@var{p}, @var{tfvar})
+## Return the string of a polynomial with string @var{tfvar} as variable.
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: September 2009
+## Version: 0.1
+
+function str = tfpoly2str (p, tfvar = "x")
+
+ str = "";
+
+ lp = numel (p.poly);
+
+ if (lp > 0)
+ ## first element (highest order)
+ a = p.poly(1);
+
+ if (a < 0)
+ cs = "-";
+ else
+ cs = "";
+ endif
+
+ if (lp == 1)
+ str = [cs, num2str(abs (a), 4)];
+ else
+ if (abs (a) == 1)
+ str = [cs, __variable__(tfvar, lp-1)];
+ else
+ str = [cs, __coefficient__(a), " ", __variable__(tfvar, lp-1)];
+ endif
+ endif
+
+ if (lp > 1)
+ ## elements in the middle
+ for k = 2 : lp-1
+ a = p.poly(k);
+
+ if (a != 0)
+ if (a < 0)
+ cs = " - ";
+ else
+ cs = " + ";
+ endif
+
+ if (abs (a) == 1)
+ str = [str, cs, __variable__(tfvar, lp-k)];
+ else
+ str = [str, cs, __coefficient__(a), " ", __variable__(tfvar, lp-k)];
+ endif
+ endif
+ endfor
+
+ ## last element (lowest order)
+ a = p.poly(lp);
+
+ if (a != 0)
+ if (a < 0)
+ cs = " - ";
+ else
+ cs = " + ";
+ endif
+
+ str = [str, cs, num2str(abs (a), 4)];
+ endif
+ endif
+ endif
+
+endfunction
+
+
+function str = __coefficient__ (a)
+
+ b = abs (a);
+
+ if (b == 1)
+ str = "";
+ else
+ str = num2str (b, 4);
+ endif
+
+endfunction
+
+
+function str = __variable__ (tfvar, n)
+
+ if (n == 1)
+ str = tfvar;
+ else
+ str = [tfvar, "^", num2str(n)];
+ endif
+
+endfunction