## [r8778]: trunk / octave-forge / main / symbolic / inst / sym2poly.m  Maximize  Restore  History

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 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157``` ```## Copyright (C) 2003 Willem J. Atsma ## ## This program 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 2, or (at your option) any later version. ## ## This software 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 this software; see the file COPYING. If not, ## see . ## -*- texinfo -*- ## @deftypefn {Function File} {@var{c} =} sym2poly (@var{p}, @var{x}) ## Returns the coefficients of the symbolic polynomial expression @var{p} ## as a vector. If there is only one free variable in @var{p} the ## coefficient vector @var{c} is a plain numeric vector. If there is more ## than one free variable in @var{p}, a second argument @var{x} specifies the ## free variable and the function returns a cell vector of symbolic expressions. ## The coefficients correspond to decreasing exponent of the free variable. ## ## Example: ## @example ## symbols ## x = sym("x"); ## y = sym("y"); ## c = sym2poly (x^2+3*x-4); # c = [1,3,-4] ## c = sym2poly (x^2+y*x,x); # c = @{2,y,0@} ## @end example ## ## If @var{p} is not a polynomial the result has no warranty. ## ## @seealso{poly2sym,polyval,roots} ## @end deftypefn ## Created: 18 April 2003 ## Changed: 25 April 2003 ## Removed the use of differentiate to get to coefficients - round-off ## errors cause problems. Now using newly created sumterms(). ## Changed: 6 May 2003 ## Removed the attempt to use ldegree(), degree() and coeff() - results ## with these are inconsistent. function c = sym2poly(p,x) BADPOLY_COEFF_LIMIT = 500; if is_vpa(p) ## polynomial is one vpa number c = to_double(p); if length(c)!=1 error("Argument is not a polynomial."); endif return endif if !is_ex(p) error("Argument has to be a symbolic expression.") endif pvars = findsymbols(p); if isempty(pvars) ## It is possible that we get an expression without any symbols. c = to_double(p); return; endif nvars = length(pvars); if nvars>1 && exist("x")!=1 error("Symbolic expression has more than 1 free variable; no variable specified.") elseif exist("x")!=1 x = pvars{1}; endif p = expand(p); ## GiNaC has commands to access coefficients directly, but in octave this often ## does not work, because for example x^2 typed in octave results in a ## non-integer power in GiNaC: x^2.0 . [num,den] = numden(p); tmp = findsymbols(den); for i=1:length(tmp) if tmp{i}==x error("Symbolic expression is a ratio of polynomials.") endif endfor p = expand(p); p_terms = sumterms(p); ## if this is well behaved, I can find the coefficients by dividing with x c_ex = cell; for i=1:length(p_terms) tmp = p_terms{i}; for j=1:BADPOLY_COEFF_LIMIT if disp(differentiate(tmp,x))=="0" break; endif tmp = tmp/x; endfor if j==BADPOLY_COEFF_LIMIT printf("Please examine your code or adjust this function.\n"); printf("This error may occur because the passed expression is not a polynomial.\n"); error("Reached the set limit (%d) for the number of coefficients.",BADPOLY_COEFF_LIMIT) endif if (length(c_ex)