### Method and device for calculating trust values on purchases

Trust values of n nodes are calculated by relating nodes having corresponding relations with arrows. Pij (i, j=1 to n) is assigned as a weight for an arrow from node ui to node uj on the basis of the relation between the nodes. P'=CPcP+(1-Cc) E is calculated, where Cc=constant, E=a predetermined matrix, pP=a matrix having elements at row i and column j represented by Pij. The trust value of each node is calculated on the basis of P'.