function [xsmooth, Vsmooth, VVsmooth, loglik] = kalman_smoother(y, A, C, Q, R, init_x, init_V, varargin)% Kalman/RTS smoother.% [xsmooth, Vsmooth, VVsmooth, loglik] = kalman_smoother(y, A, C, Q, R, init_x, init_V, ...)%% The inputs are the same as for kalman_filter.% The outputs are almost the same, except we condition on y(:, 1:T) (and u(:, 1:T) if specified),% instead of on y(:, 1:t).[os T] = size(y);ss = length(A);% set default paramsmodel = ones(1,T);u = [];B = [];args = varargin;nargs = length(args);for i=1:2:nargs  switch args{i}   case 'model', model = args{i+1};   case 'u', u = args{i+1};   case 'B', B = args{i+1};   otherwise, error(['unrecognized argument ' args{i}])  endendxsmooth = zeros(ss, T);Vsmooth = zeros(ss, ss, T);VVsmooth = zeros(ss, ss, T);% Forward pass[xfilt, Vfilt, VVfilt, loglik] = kalman_filter(y, A, C, Q, R, init_x, init_V, ...					       'model', model, 'u', u, 'B', B); %調(diào)用了kalman_filter，kalman_update% Backward passxsmooth(:,T) = xfilt(:,T);Vsmooth(:,:,T) = Vfilt(:,:,T);%VVsmooth(:,:,T) = VVfilt(:,:,T);for t=T-1:-1:1  m = model(t+1);  if isempty(B)    [xsmooth(:,t), Vsmooth(:,:,t), VVsmooth(:,:,t+1)] = ...	smooth_update(xsmooth(:,t+1), Vsmooth(:,:,t+1), xfilt(:,t), Vfilt(:,:,t), ...		      Vfilt(:,:,t+1), VVfilt(:,:,t+1), A(:,:,m), Q(:,:,m), [], []);  else    [xsmooth(:,t), Vsmooth(:,:,t), VVsmooth(:,:,t+1)] = ...	smooth_update(xsmooth(:,t+1), Vsmooth(:,:,t+1), xfilt(:,t), Vfilt(:,:,t), ...		      Vfilt(:,:,t+1), VVfilt(:,:,t+1), A(:,:,m), Q(:,:,m), B(:,:,m), u(:,t+1));  endendVVsmooth(:,:,1) = zeros(ss,ss);