Making and Modifying Graphs

add_edge!(g, e)

Add an edge e to graph g. Return true if edge was added successfully, otherwise return false.

Examples

julia> using LightGraphs

julia> g = SimpleGraph(2);

julia> add_edge!(g, 1, 2)
true

julia> add_edge!(g, 2, 3)
false

rem_edge!(g, e)

Remove an edge e from graph g. Return true if edge was removed successfully, otherwise return false.

Implementation Notes

If rem_edge! returns false, the graph may be in an indeterminate state, as there are multiple points where the function can exit with false.

Examples

julia> using LightGraphs

julia> g = SimpleGraph(2);

julia> add_edge!(g, 1, 2);

julia> rem_edge!(g, 1, 2)
true

julia> rem_edge!(g, 1, 2)
false

add_vertex!(g)

Add a new vertex to the graph g. Return true if addition was successful.

Examples

julia> using LightGraphs

julia> g = SimpleGraph(Int8(typemax(Int8) - 1))
{126, 0} undirected simple Int8 graph

julia> add_vertex!(g)
true

julia> add_vertex!(g)
false

add_vertices!(g, n)

Add n new vertices to the graph g. Return the number of vertices that were added successfully.

Examples

julia> using LightGraphs

julia> g = SimpleGraph()
{0, 0} undirected simple Int64 graph

julia> add_vertices!(g, 2)
2

rem_vertex!(g, v)

Remove the vertex v from graph g. Return false if removal fails (e.g., if vertex is not in the graph); true otherwise.

Performance

Time complexity is $\mathcal{O}(k^2)$, where $k$ is the max of the degrees of vertex $v$ and vertex $|V|$.

Implementation Notes

This operation has to be performed carefully if one keeps external data structures indexed by edges or vertices in the graph, since internally the removal is performed swapping the vertices v and $|V|$, and removing the last vertex $|V|$ from the graph. After removal the vertices in g will be indexed by $1:|V|-1$.

Examples

julia> using LightGraphs

julia> g = SimpleGraph(2);

julia> rem_vertex!(g, 2)
true

julia> rem_vertex!(g, 2)
false

zero(G)

Return a zero-vertex, zero-edge version of the graph type G. The fallback is defined for graph values zero(g::G) = zero(G).

Examples

julia> g = SimpleDiGraph([0 1 0 0 0; 0 0 1 0 0; 1 0 0 1 0; 0 0 0 0 1; 0 0 0 1 0]);

julia> zero(typeof(g))
{0, 0} directed simple Int64 graph

julia> zero(g)
{0, 0} directed simple Int64 graph