check_graph — checks a Scilab graph data structure
check_graph(g [,opt])
check_graph(g,%f) checks its argument g to see if it is a
valid graph_data_structure. 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.
check_graph(g,%t) also check graphics and data fields validity.