function of = a0asfun(x,s,nobs,nvar,a0indx)
% General program to setup A0 matrix with asymmetric prior (as) and compute the posterior
%     function of = a0asfun(x,s,nobs,nvar,a0indx) -- negative logPosterior
%        Note: columns correspond to equations
%  x (parameter vector),
%  s (diag(S1,...,Sm)): note, as in "a0lhfun", already divided by "nobs"
%  nobs (no of obs),
%  nvar (no of variables),
%  a0indx (matrix indicating the free parameters in A0, and each column in A0 corresponds
%                    to an equation)
%
% Copyright (c) December 1997 by Tao Zha
%

a0 = zeros(nvar);
a0(a0indx) = x;
% Note: each column in a0 corresponds to an equation!!
%
%%ada = chol(a0'*a0);
%%ada = log(abs(diag(ada)));
%%ada = sum(ada);
% **  TZ, 10/15/96, the above two lines can be improved by the following three lines
[a0l,a0u] = lu(a0);
%ada=diag(abs(a0u));
%ada=sum(log(ada));
ada = sum(log(abs(diag(a0u))));

%
%tra = sum(i=1:m){a0(:,i)'*Si*a0(:,i)}
tra = 0.0;
for i=1:nvar
   tra = tra + a0(:,i)'*s{i}*a0(:,i);
end

of = -nobs*ada + nobs*.5*tra;