check_graph - checks a Scilab graph list
check_graph checks its argument g to see if it is a graph list. The checking is not only syntactic (number of elements of the list, compatible sizes of the vectors), but also semantic in the sense that check_graph checks that node_number, tail and head elements of the list can really represent a graph.
Moreover, the names of the node must be different. In fact, this do not give errors in Scilab, but strange behaviour can appear when using the Metanet window. So, this is not checked by check_graph because it is time consuming. It is only checked when loading, saving or showing a graph.