On the right-hand side of the dialog box, there is a picture illustrating the chosen algorithm. When you change the algorithm by using the “Algorithm” popup menu, the picture changes accordingly.

The purpose of this picture is to assist you in choosing the right algorithm. The circles labelled “G” represent the predecessors of the node. Although there are typically three such circles, this does not at all mean that there have to be exactly three predecessors. A node can of course have any number of predecessors you want. The circle labelled “Loc” represents the local value of the node. The arrows reflect the order in which the operators are applied.