The prior updating algorithm. A) Pseudo-code for the algorithm is shown. A free parameter α in the updating equation is used to determine the degree of change of priors. When α is zero, the priors do not change and the graphical model results are the same as the results of the base classifier. The priors are pushed harder to the majority classes in the field as α increases. B) Illustration of the PU algorithm for a graphical network of seven cells and three classes.