replace func sum with +, for only two elements added.
bug fixed: when only one edge exists in the graph, no need for checking multiple edges.
randomly select one node from a set where nodes possess same degree
bug fix for counting percentage.
add: showing percentage of task.
percentage showing bug fix for decimal fraction
nothing changed
write edge list to pajek format file.
bug fix: assertion
count the edges.
annotations ok, function not finished.