function gamma=atog(a)
%ATOG	Step-down recursion
%----
%USAGE: gamma=atog(a)
%
%	Finds the reflection coefficients gamma from the
%	direct-form filter coefficients a(k).
%
%  see also ATOR, GTOA, GTOR, RTOA, RTOG
%
%---------------------------------------------------------------
% copyright 1996, by M.H. Hayes.  For use with the book 
% "Statistical Digital Signal Processing and Modeling"
% (John Wiley & Sons, 1996).
%---------------------------------------------------------------

a=a(:);
p=length(a);
a=a(2:p)/a(1);
gamma(p-1)=a(p-1);
for j=p-1:-1:2;
	a=(a(1:j-1) - gamma(j)*flipud(conj(a(1:j-1))))./ ...
	  (1 - abs(gamma(j))^2);
	gamma(j-1)=a(j-1);
	end
