hnstm=sgsdf_even_gram_poly(n,s,t,m)

function hnstm=sgsdf_even_gram_poly(n,s,t,m)
% Savitzky-Golay Smoothing and Differentiation Filter of Even Length
%
% hnstm=sgsdf_gram_poly(n,s,t,m)
% n:      polynomial degree
% s:      derivative(differentiation) order (0=smoothing)
% t:      evaluation point (commonly,t=0,i.e.,smoothing or differentiation
%               at the imaginary central point of the 2*m points)
% 2*m:    data point number,i.e., filter length
% hnstm:  convoluction coefficients  
%
% Author:
% Jianwen Luo <[e-mail]> 2005-06-12
% Department of Biomedical Engineering
% Tsinghua University, Beijing 100084, P. R. China 
%
% References: 
% [1]	Luo J W, Ying K, Bai J. 
%     Savitzky-Golay Smoothing and Differentiation Filter for Even Number Data, 
%     Signal Process. 2005, 85(7): 1429-1434
% [2]	Luo J W, Bai J. 
%     Savitzky-Golay Smoothing and Differentiation Filter of Even Length: A Gram Polynomial Approach, 
%     Spectroscopy. 2005, in press

hnstm=[];
for i=-m+1/2:m-1/2
    hnstm=[hnstm hinstm(i,n,s,t,m)];
end