Use this if you are using igraph from R
Simple graphs are graphs which do not contain loop and multiple edges.
simplify( graph, remove.multiple = TRUE, remove.loops = TRUE, edge.attr.comb = igraph_opt("edge.attr.comb") ) is_simple(graph) simplify_and_colorize(graph)
graph 
The graph to work on. 
remove.multiple 
Logical, whether the multiple edges are to be removed. 
remove.loops 
Logical, whether the loop edges are to be removed. 
edge.attr.comb 
Specifies what to do with edge attributes, if

A loop edge is an edge for which the two endpoints are the same vertex. Two edges are multiple edges if they have exactly the same two endpoints (for directed graphs order does matter). A graph is simple is it does not contain loop edges and multiple edges.
is_simple
checks whether a graph is simple.
simplify
removes the loop and/or multiple edges from a graph. If
both remove.loops
and remove.multiple
are TRUE
the
function returns a simple graph.
simplify_and_colorize
constructs a new, simple graph from a graph and
also sets a color
attribute on both the vertices and the edges.
The colors of the vertices represent the number of selfloops that were
originally incident on them, while the colors of the edges represent the
multiplicities of the same edges in the original graph. This allows one to
take into account the edge multiplicities and the number of loop edges in
the VF2 isomorphism algorithm. Other graph, vertex and edge attributes from
the original graph are discarded as the primary purpose of this function is
to facilitate the usage of multigraphs with the VF2 algorithm.
a new graph object with the edges deleted.
Gabor Csardi csardi.gabor@gmail.com
which_loop
, which_multiple
and
count_multiple
, delete_edges
,
delete_vertices
g < graph( c(1,2,1,2,3,3) ) is_simple(g) is_simple(simplify(g, remove.loops=FALSE)) is_simple(simplify(g, remove.multiple=FALSE)) is_simple(simplify(g))