function y = tau ( x )

%% TAU evaluates a polynomial.
%
%  tau(x) is actually the Chebyshev polynomial of the first kind, of degree 10.
%
%  The smallest root of this polynomial is approximately 0.1564344...
%
%  X is the evaluation point.
%
%  Y is the value.
%
%  X can be a vector.
%
  y =  512 * x.^10 ...
    - 1280 * x.^8 ...
    + 1120 * x.^6 ...
    -  400 * x.^4 ...
    +   50 * x.^2 ...
    -    1;

  return
end