diff toolboxes/FullBNT-1.0.7/bnt/inference/static/@pearl_inf_engine/private/compute_bel.m @ 0:e9a9cd732c1e tip

first hg version after svn

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolboxes/FullBNT-1.0.7/bnt/inference/static/@pearl_inf_engine/private/compute_bel.m	Tue Feb 10 15:05:51 2015 +0000
@@ -0,0 +1,24 @@
+function bel = compute_bel(msg_type, pi, lambda)
+
+switch msg_type,
+ case 'd', bel = normalise(pi .* lambda);
+ case 'g',
+  if isinf(lambda.precision) % ignore pi because lambda is completely certain (observed)
+    bel.mu = lambda.mu;
+    bel.Sigma = zeros(length(bel.mu)); % infinite precision => 0 variance
+  elseif all(pi.Sigma==0) % ignore lambda because pi is completely certain (delta fn prior)
+    bel.Sigma = pi.Sigma;
+    bel.mu = pi.mu;
+  elseif all(isinf(pi.Sigma)) % ignore pi because pi is completely uncertain
+    bel.Sigma  = inv(lambda.precision);
+    bel.mu = bel.Sigma * lambda.info_state;
+  elseif all(lambda.precision == 0) % ignore lambda because lambda is completely uncertain
+    bel.Sigma = pi.Sigma;
+    bel.mu = pi.mu;
+  else % combine both pi and lambda
+    pi_precision = inv(pi.Sigma);
+    bel.Sigma = inv(pi_precision + lambda.precision);
+    bel.mu = bel.Sigma*(pi_precision * pi.mu + lambda.info_state);
+  end
+ otherwise, error(['unrecognized msg type ' msg_type])
+end