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## Copyright (C) 2012 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: May 2012
## Version: 0.1
function str = tfpoly2str (p, tfvar = "x")
## TODO: simplify this ugly code
str = "";
lp = numel (p);
if (lp > 0) # first element (lowest order)
idx = find (p); # first non-zero element
if (isempty (idx))
str = "0";
return;
else
idx = idx(1);
endif
a = p(idx);
if (a < 0)
cs = "-";
else
cs = "";
endif
if (idx == 1)
str = [cs, num2str(abs (a), 4)];
else
if (abs (a) == 1)
str = [cs, __variable__(tfvar, idx-1)];
else
str = [cs, __coefficient__(a), " ", __variable__(tfvar, idx-1)];
endif
endif
if (lp > idx) # remaining elements of higher order
for k = idx+1 : lp
a = p(k);
if (a != 0)
if (a < 0)
cs = " - ";
else
cs = " + ";
endif
if (abs (a) == 1)
str = [str, cs, __variable__(tfvar, k-1)];
else
str = [str, cs, __coefficient__(a), " ", __variable__(tfvar, k-1)];
endif
endif
endfor
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)
str = [tfvar, "^-", num2str(n)];
endfunction
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