function [f, df] = Pn(c,x)
% function [f, df] = Pn(c,x)
% 
%
%
%
%

n  = columns(c);
f  = c(1);
df = c(1);
for i = 2:n-1
    f = x*f + c(i);
   df = x*df+ f;
endfor
f = x*f + c(n);