# Copyright (C) 1995 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, 675 Mass Ave, Cambridge, MA 02139, USA.

function y = polyvalm (c, x)

# usage: polyvalm (c, x)
#
# Evaluate a polynomial in the matrix sense.
#
# In octave, a polynomial is represented by it's coefficients (arranged
# in descending order). For example a vector c of length n+1 corresponds
# to the following nth order polynomial
#
#   p(x) = c(1) x^n + ... + c(n) x + c(n+1).
#
# polyvalm(c,X) will evaluate the polynomial in the matrix sense, i.e. matrix
# multiplication is used instead of element by element multiplication as is
# used in polyval.
#
# X must be a square matrix.
#
# SEE ALSO: polyval, poly, roots, conv, deconv, residue, filter,
#           polyderiv, polyinteg

# Written by Tony Richardson (amr@mpl.ucsd.edu) June 1994.

  if(nargin != 2)
    usage ("polyvalm (c, x)");
  endif

  if (is_matrix (c))
    error("poly: first argument must be a vector.");
  endif

  if(! is_square (x))
    error("poly: second argument must be a square matrix.");
  endif

  [v, d] = eig(x);

  y = v * diag (polyval (c, diag (d))) * v';

endfunction