function ds=chdx(s);

% The function ds=ledx(s) computes the first derivative of truncated Chebyshev series expansion.
%  Input: 
%    s--Chebyshev coefficients 
%  output: 
%    ds--Chebyshev coefficients of 1st-order derivative

nn=length(s);
n=nn-1;

ds=[];
ds(nn)=0;ds(nn-1)=2*n*s(nn);
for k=n-1:-1:1,
	ds(k)=ds(k+2)+2*k*s(k+1);
end; 
ds(1)=ds(1)*.5d0;
ds=ds';
if size(s,1)<size(s,2), ds=ds'; end;