annotate scripts/polynomial/polygcd.m @ 17420:95bfa04ab514

Fix bug in colorbar demo #24. set() is broken from deep within listener hierarchy. Workaround it. * scripts/plot/colorbar.m(update_colorbar_clim): Set axis limits in listener and then jiggle the axis position to force a redraw.
author Rik <rik@octave.org>
date Wed, 11 Sep 2013 16:05:40 -0700
parents 5d3a684236b0
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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72c96de7a403 maint: update copyright notices for 2012
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1 ## Copyright (C) 2000-2012 Paul Kienzle
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {@var{q} =} polygcd (@var{b}, @var{a})
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21 ## @deftypefnx {Function File} {@var{q} =} polygcd (@var{b}, @var{a}, @var{tol})
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22 ##
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23 ## Find the greatest common divisor of two polynomials. This is equivalent
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24 ## to the polynomial found by multiplying together all the common roots.
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25 ## Together with deconv, you can reduce a ratio of two polynomials.
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26 ## The tolerance @var{tol} defaults to @code{sqrt (eps)}.
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27 ##
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28 ## @strong{Caution:} This is a numerically unstable algorithm and should not
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29 ## be used on large polynomials.
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30 ##
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31 ## Example code:
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32 ##
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33 ## @example
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34 ## @group
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35 ## polygcd (poly (1:8), poly (3:12)) - poly (3:8)
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36 ## @result{} [ 0, 0, 0, 0, 0, 0, 0 ]
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37 ## deconv (poly (1:8), polygcd (poly (1:8), poly (3:12))) - poly (1:2)
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38 ## @result{} [ 0, 0, 0 ]
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39 ## @end group
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40 ## @end example
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41 ## @seealso{poly, roots, conv, deconv, residue}
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42 ## @end deftypefn
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43
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44 function x = polygcd (b, a, tol)
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45
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46 if (nargin == 2 || nargin == 3)
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47 if (nargin == 2)
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48 if (isa (a, "single") || isa (b, "single"))
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49 tol = sqrt (eps ("single"));
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50 else
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51 tol = sqrt (eps);
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52 endif
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53 endif
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54 if (length (a) == 1 || length (b) == 1)
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55 if (a == 0)
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56 x = b;
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57 elseif (b == 0)
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58 x = a;
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59 else
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60 x = 1;
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61 endif
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62 else
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63 a /= a(1);
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64 while (1)
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65 [d, r] = deconv (b, a);
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66 nz = find (abs (r) > tol);
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67 if (isempty (nz))
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68 x = a;
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69 break;
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70 else
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71 r = r(nz(1):length(r));
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72 endif
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73 b = a;
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74 a = r / r(1);
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75 endwhile
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76 endif
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77 else
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78 print_usage ();
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79 endif
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80
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81 endfunction
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82
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83
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84 %!test
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85 %! poly1 = [1 6 11 6]; # (x+1)(x+2)(x+3);
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86 %! poly2 = [1 3 2]; # (x+1)(x+2);
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87 %! poly3 = polygcd (poly1, poly2);
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88 %! assert (poly3, poly2, sqrt (eps));
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89
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90 %!assert (polygcd (poly (1:8), poly (3:12)), poly (3:8), sqrt (eps))
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91 %!assert (deconv (poly (1:8), polygcd (poly (1:8), poly (3:12))), poly (1:2), sqrt (eps))
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92
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93 %!test
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94 %! for ii=1:10
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95 %! p = (unique (randn (10, 1)) * 10).';
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96 %! p1 = p(3:end);
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97 %! p2 = p(1:end-2);
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98 %! assert (polygcd (poly (-p1), poly (-p2)), poly (- intersect (p1, p2)), sqrt (eps));
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99 %! endfor
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100