# Prop Sum Fast Retract

The prop sum fast retract propagation can be activated if you are using auto propagation, you can specify HUGIN to use this propagation method. The “prop sum fast retract” propagation method can be used in HUGIN networks (Bayesian networks object-oriented Bayesian networks) containing only discrete chance nodes. It is similar to the sum normal method except that it shows the nodes which have received evidence differently. Instead of showing the true posterior probability distribution for the node, the distribution is shown as if the node had not received evidence. That is, the distribution shown is the posterior probability distribution given the evidence entered in all other nodes. To indicate that the node has in fact received evidence, the belief bars are painted using the color code for evidence (default: Red).

This propagation method can be used to check if the evidence entered in a node meets the probabilities of the evidence or if there are signs of some kind of conflict (the evidence entered is one of the most unlikely states of the node).