Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / symbolic-1.1.0 / poly2sym.m

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+## Copyright (C) 2003 Willem J. Atsma <watsma@users.sf.net>
+##
+## 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 <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{p} =} poly2sym (@var{c}, @var{x})
+## Creates a symbolic polynomial expression @var{p} with coefficients @var{c}.
+## If @var{p} is not specified, the free variable is set to sym("x"). @var{c}
+## may be a vector or a cell-array of symbols. @var{x} may be a symbolic
+## expression or a string.
+## The coefficients correspond to decreasing exponent of the free variable.
+##
+## Example:
+## @example
+## symbols
+## x = sym("x");
+## y = sym("y");
+## p = poly2sym ([2,5,-3]);         # p = 2*x^2+5*x-3
+## c = poly2sym (@{2*y,5,-3@},x);     # p = 2*y*x^2+5*x-3
+## @end example
+##
+## @seealso{sym2poly,polyval,roots}
+## @end deftypefn
+
+function p = poly2sym(c,x)
+
+  if exist("x")!=1
+    x = sym("x");
+  endif
+
+  N = length(c);
+
+  if !iscell(c)
+    tmp = c;
+    c = cell;
+    for i=1:N
+      c(i) = tmp(i);
+    endfor
+  endif
+
+  p = vpa(0);
+  for i=1:N
+    if isnumeric(c{i})
+      p = p*x+vpa(c{i});
+    else
+      p = p*x+c{i};
+    endif
+  endfor
+
+endfunction