function Sep25()

% Fact:  T_{0}(z) = 1; T_{1}(z) = z; 
%        T_{k}(z) = 2z*T_{k-1}(z) - T_{k-2}(z)

% So:    T'_{0}(z) = 0 T'_{1}(z) = 1;
%        T'_{k}(z) = 2T_{k-1}(z) + 2z*T'_{k-1} - T'_{k-2}
% 
% Fact: (d/dx)T_{k}(-1+2(x-a)/(b-a)) = ((b-a)/2)T'_{k}(-1+2(x-a)/(b-a))

  function yp = DerPoly(a,b,alfa,x0)
% a nd b are scalars with a<b.
% x0 is a scalar
% alfa is a column (n+1) vector
% yp = p'(x0) where
%  p(x) = alfa(1)T_{0}(-1+2(x-a)/(b-a)) + ... +
%         alfa(n+1)T_{n}(-1+2(x-a)/(b-a))
