polyval.m

JAVA 数学程序库 提供常规的数值计算程序包

## Copyright (C) 1996, 1997 John W. Eaton
##
## This file is part of Octave.
##
## Octave 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.
##
## Octave 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 Octave; see the file COPYING.  If not, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301, USA.

## -*- texinfo -*-
## @deftypefn {Function File} {} polyval (@var{c}, @var{x})
## Evaluate a polynomial.
##
## @code{polyval (@var{c}, @var{x})} will evaluate the polynomial at the
## specified value of @var{x}.
##
## If @var{x} is a vector or matrix, the polynomial is evaluated at each of
## the elements of @var{x}.
## @seealso{polyvalm, poly, roots, conv, deconv, residue, filter,
## polyderiv, polyinteg}
## @end deftypefn

## Author: Tony Richardson <[e-mail]>
## Created: June 1994
## Adapted-By: jwe

function y = polyval (c, x)

  if (nargin != 2)
    print_usage ();
  endif

  if (! (isvector (c) || isempty (c)))
    error ("polyval: first argument must be a vector");
  endif

  if (isempty (x))
    y = [];
    return;
  endif

  if (length (c) == 0)
    y = c;
    return;
  endif

  n = length (c);
  y = c (1) * ones (rows (x), columns (x));
  for index = 2:n
    y = c (index) + x .* y;
  endfor

endfunction

/*
@GROUP
polynomial
@SYNTAX
y = polyval (c, x)
@DOC
.
@NOTES
@EXAMPLES
@SEE
poly, polyreduce, polyinteg, roots, unmkpp
*/