Mercurial > hg > octave-lyh
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> |
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date | Wed, 11 Sep 2013 16:05:40 -0700 |
parents | 5d3a684236b0 |
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rev | line source |
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1 ## Copyright (C) 2000-2012 Paul Kienzle |
5216 | 2 ## |
7016 | 3 ## This file is part of Octave. |
5216 | 4 ## |
7016 | 5 ## Octave is free software; you can redistribute it and/or modify it |
6 ## under the terms of the GNU General Public License as published by | |
7 ## the Free Software Foundation; either version 3 of the License, or (at | |
8 ## your option) any later version. | |
9 ## | |
10 ## Octave is distributed in the hope that it will be useful, but | |
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 ## General Public License for more details. | |
5216 | 14 ## |
15 ## You should have received a copy of the GNU General Public License | |
7016 | 16 ## along with Octave; see the file COPYING. If not, see |
17 ## <http://www.gnu.org/licenses/>. | |
5216 | 18 |
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}) |
5216 | 22 ## |
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23 ## Find the greatest common divisor of two polynomials. This is equivalent |
5216 | 24 ## to the polynomial found by multiplying together all the common roots. |
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)}. |
5216 | 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 ## |
5216 | 33 ## @example |
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34 ## @group |
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35 ## polygcd (poly (1:8), poly (3:12)) - poly (3:8) |
6850 | 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) |
6850 | 38 ## @result{} [ 0, 0, 0 ] |
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39 ## @end group |
5216 | 40 ## @end example |
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41 ## @seealso{poly, roots, conv, deconv, residue} |
5642 | 42 ## @end deftypefn |
5216 | 43 |
5217 | 44 function x = polygcd (b, a, tol) |
45 | |
46 if (nargin == 2 || nargin == 3) | |
47 if (nargin == 2) | |
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48 if (isa (a, "single") || isa (b, "single")) |
10549 | 49 tol = sqrt (eps ("single")); |
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50 else |
10549 | 51 tol = sqrt (eps); |
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52 endif |
5216 | 53 endif |
5217 | 54 if (length (a) == 1 || length (b) == 1) |
55 if (a == 0) | |
10549 | 56 x = b; |
5217 | 57 elseif (b == 0) |
10549 | 58 x = a; |
5217 | 59 else |
10549 | 60 x = 1; |
5217 | 61 endif |
62 else | |
63 a /= a(1); | |
64 while (1) | |
10549 | 65 [d, r] = deconv (b, a); |
66 nz = find (abs (r) > tol); | |
67 if (isempty (nz)) | |
68 x = a; | |
69 break; | |
70 else | |
71 r = r(nz(1):length(r)); | |
72 endif | |
73 b = a; | |
74 a = r / r(1); | |
5217 | 75 endwhile |
76 endif | |
77 else | |
6046 | 78 print_usage (); |
5216 | 79 endif |
5217 | 80 |
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 |