function of = fn_a0sfreefun(b,Uistar,Uibar,nvar,nStates,n0,Tkave,Sgm0tldinvave)
% of = fn_a0sfreefun(b,Uistar,Uibar,nvar,nStates,n0,Tkave,Sgm0tldinvave)
%  Negative logPosterior function for regime-switching squeesed free A0 parameters,
%    which are b's in the WZ notation. The case of no asymmetric prior and no lag restrictions.
%    Note: (1) columns correspond to equations; s stands for state.
%    See TBVAR NOTE pp.34-34a,38.
%
% b: sum(n0)*nStates-by-1 vector of free A0 parameters, vectorized from the sum(n0)-by-nStates matrix.
% Uistar: cell(nvar,1).  In each cell, nvar*nSates-by-qi orthonormal basis for the null of the ith
%           equation contemporaneous restriction matrix where qi is the number of free parameters.
%           With this transformation, we have ai = Ui*bi or Ui'*ai = bi where ai is a vector
%           of total original parameters and bi is a vector of free parameters. When no
%           restrictions are imposed, we have Ui = I.  There must be at least one free
%           parameter left for the ith equation.  See p.33.
% Uibar: cell(nvar,1).  In each cell, we have nvar*nStates-by-qi*nStates, rearranged
%           from Uistar or Ui.  See p.33.  This is NOT used for this function, but serves as an argument
%           to keep it compatible with fn_a0sfreegrad.m which uses it.
% nvar:  Number of endogeous variables.
% nStates:  NUmber of states.
% n0: nvar-by-1, ith element represents the number of free A0 parameters in ith equation for each state.
% Tkave: nStates-by-1 of sample sizes (excluding lags but including dummies if provided) for different states k,
%           averaged (ave) over E-step draws.  For T_k.  See p.38.
% Sgm0tldinvave:  nvar*nStates-by-nvar*nStates.  The matrix inv(\Sigma~_0) averaged (ave)
%         over E-step draws. Same for all equations because of no asymmetric prior and no lag
%         restrictions.  Resembles old SpH in the exponent term in posterior of A0,
%         but NOT divided by fss (T) yet.  See p.38.
%----------------
% of:  Objective function (negative logPosterior).
%
% This function is a special case of fn_a0sfreefun2.m.
% Tao Zha, March 2001


n0=n0(:);
A0=zeros(nvar,nvar,nStates);
n0cum = [0;cumsum(n0)];
b=reshape(b,n0cum(end),nStates);

tra = 0.0;
for kj = 1:nvar
   lenbjs=length(n0cum(kj)+1:n0cum(kj+1));
   bj = zeros(nStates*lenbjs,1);
   a0j = zeros(nStates*nvar,1);  % See p.33.
   for si=1:nStates
      bj((si-1)*lenbjs+1:si*lenbjs) = b(n0cum(kj)+1:n0cum(kj+1),si);  % bj(si).  See p.34a.
      A0(:,kj,si) = Uistar{kj}((si-1)*nvar+1:si*nvar,:)*b(n0cum(kj)+1:n0cum(kj+1),si);
      a0j((si-1)*nvar+1:si*nvar) = A0(:,kj,si);   % a0j(si).  See p.33.
   end
   %tra = tra + 0.5*a0j'*Sgm0tldinvave*a0j;   % negative exponential term
   tra = tra+0.5*bj'*(Uibar{kj}'*Sgm0tldinvave*Uibar{kj})*bj;
end

ada=0.0;
for si=1:nStates     % See p.34a.
   [A0l,A0u] = lu(A0(:,:,si));
   ada = ada - Tkave(si)*sum(log(abs(diag(A0u))));    % negative log determinant of A0 raised to power T
end

of = ada + tra;