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## -*- texinfo -*-
## @deftypefn {} {@var{y} =} polyvalm (@var{c}, @var{x})
## Evaluate a polynomial in the matrix sense.
##
## @code{polyvalm (@var{c}, @var{x})} will evaluate the polynomial in the
## matrix sense, i.e., matrix multiplication is used instead of element by
## element multiplication as used in @code{polyval}.
##
## The argument @var{x} must be a square matrix.
## @seealso{polyval, roots, poly}
## @end deftypefn

function y = polyvalm (c, x)

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

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

  if (! issquare (x))
    error ("polyvalm: second argument must be a square matrix");
  endif

  n = length (c);
  if (n == 0)
    y = zeros (rows (x), class (x));
  else
    id = eye (rows (x), class (x));
    y = c(1) * id;
    for i = 2:n
      y = y * x + c(i) * id;
    endfor
  endif

endfunction


%!assert (! any (polyvalm ([], [1, 2; 3, 4]))(:))
%!assert (polyvalm ([1, 2, 3, 4], [3, -4, 1; -2, 0, 2; -1, 4, -3]),
%!        [117, -124, 11; -70, 36, 38; -43, 92, -45])

%!error <must be a square matrix> polyvalm ([1, 1, 1], [1, 2; 3, 4; 5, 6])