function r = a2r( a )
% function r = a2r( a )
% 
% Convert Predictor Coefficients to Reflexion Coefficients
%
% Author: Markus Hauenstein
% Date:   30.12.2001

a = a(:);
P = length( a );
A = zeros(P,P);
A(:,P) = a;
r = zeros(P,1);

r(P) = A(P,P);

for m = P:-1:2,
  for i = 1:m-1,
     A(i,m-1) = (A(i,m) + r(m) * A(m-i,m)) / (1-r(m)*r(m));
     r(m-1) = A(m-1,m-1);
  end
end