Mercurial > hg > camir-aes2014
diff toolboxes/FullBNT-1.0.7/bnt/CPDs/@gmux_CPD/CPD_to_lambda_msg.m @ 0:e9a9cd732c1e tip
first hg version after svn
author | wolffd |
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date | Tue, 10 Feb 2015 15:05:51 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/toolboxes/FullBNT-1.0.7/bnt/CPDs/@gmux_CPD/CPD_to_lambda_msg.m Tue Feb 10 15:05:51 2015 +0000 @@ -0,0 +1,62 @@ +function lam_msg = CPD_to_lambda_msg(CPD, msg_type, n, ps, msg, p, evidence) +% CPD_TO_LAMBDA_MSG Compute lambda message (gmux) +% lam_msg = compute_lambda_msg(CPD, msg_type, n, ps, msg, p, evidence) +% Pearl p183 eq 4.52 + +% Let Y be this node, X1..Xn be the cts parents and M the discrete switch node. +% e.g., for n=3, M=1 +% +% X1 X2 X3 M +% \ +% \ +% Y +% +% So the only case in which we send an informative message is if p=1=M. +% To the other cts parents, we send the "know nothing" message. + +switch msg_type + case 'd', + error('gaussian_CPD can''t create discrete msgs') + case 'g', + cps = ps(CPD.cps); + cpsizes = CPD.sizes(CPD.cps); + self_size = CPD.sizes(end); + i = find_equiv_posns(p, cps); % p is n's i'th cts parent + psz = cpsizes(i); + dps = ps(CPD.dps); + M = evidence{dps}; + if isempty(M) + error('gmux node must have observed discrete parent') + end + P = msg{n}.lambda.precision; + if all(P == 0) | (cps(M) ~= p) % if we know nothing, or are sending to a disconnected parent + lam_msg.precision = zeros(psz, psz); + lam_msg.info_state = zeros(psz, 1); + return; + end + % We are sending a message to the only effectively connected parent. + % There are no other incoming pi messages. + Bmu = CPD.mean(:,M); + BSigma = CPD.cov(:,:,M); + Bi = CPD.weights(:,:,M); + if (det(P) > 0) | isinf(P) + if isinf(P) % Y is observed + Sigma_lambda = zeros(self_size, self_size); % infinite precision => 0 variance + mu_lambda = msg{n}.lambda.mu; % observed_value; + else + Sigma_lambda = inv(P); + mu_lambda = Sigma_lambda * msg{n}.lambda.info_state; + end + C = inv(Sigma_lambda + BSigma); + lam_msg.precision = Bi' * C * Bi; + lam_msg.info_state = Bi' * C * (mu_lambda - Bmu); + else + % method that uses matrix inversion lemma + A = inv(P + inv(BSigma)); + C = P - P*A*P; + lam_msg.precision = Bi' * C * Bi; + D = eye(self_size) - P*A; + z = msg{n}.lambda.info_state; + lam_msg.info_state = Bi' * (D*z - D*P*Bmu); + end +end