function f = polyn( x, n )
%POLYN  Evaluate expanded form of (x-1)^n
%
%   polyn( x, n ) = ( x - 1 )^n = x^n - n*x^(n-1) + ...
%
% evaluated in expanded form.
%
% Simple little function for testing sensistivity of
% polynomial roots computed via 'fzero()'.
%
% Typical usage:
%
%   >> fzero( 'polyn', [ .1 1.7 ], [], [], 3 )
%
% which searches for root of polyn(x,3) on [ .1, 1.7 ]
% using default tolerance and no verbose tracing.
%
% See also FZERO.
%
% C.G. (11-97)
%
switch n
  case 1
    f = x - 1 ;
  case 3
    f = x.^3 - 3 * x.^2 + 3 * x - 1 ;
  case 5
    f = x.^5 - 5 * x.^4 + 10 * x.^3 - 10 * x.^2 + 5 * x - 1 ;
  otherwise
    disp(' ')
    disp('bad degree for polynomial')
    f = 0 ;
end