Marked graphs and Euler graphs
In this paper an algorithm to find all the subsets of places of a marked graph which are both siphon and trap using sign incidence matrix is proposed. We introduce a new matrix called the siphon-trap matrix for marked graphs. An interesting relation between sign incidence matrix and siphon-trap matrix is established. It is proved that the token count remains the same under any firing for the set of places which are both siphon and trap. As an application an elegant characterization for Euler graphs is obtained.