graph.constructors {igraph} | R Documentation |
These method can create various (mostly regular) graphs: empty graphs, graphs with the given edges, graphs from adjacency matrices, star graphs, lattices, rings, trees.
graph.empty(n=0, directed=TRUE) graph(edges, n=max(edges)+1, directed=TRUE) graph.star(n, mode = "in", center = 0) graph.lattice(dimvector, nei = 1, directed = FALSE, mutual = FALSE, circular = FALSE) graph.lattice(length, dim, nei = 1, directed = FALSE, mutual = FALSE, circular = FALSE) graph.ring(n, directed = FALSE, mutual = FALSE, circular=TRUE) graph.tree(n, children = 2, mode="out") graph.full(n, directed = FALSE, loops = FALSE) graph.full.citation(n, directed = TRUE) graph.atlas(n) graph.edgelist(el, directed=TRUE) graph.extended.chordal.ring(n, w)
edges |
Numeric vector defining the edges, the first edge points from the first element to the second, the second edge from the third to the fourth, etc. |
directed |
Logical, if TRUE a directed graph will be
created. Note that for while most constructors the default is TRUE,
for graph.lattice and graph.ring it is FALSE. For
graph.star the mode argument should be used for
creating an undirected graph. |
n |
The number of vertices in the graph for most functions.
For graph this parameter is ignored if there is a bigger
vertex id in edges . This means that for this function it is
safe to supply zero here if the vertex with the largest id is not an
isolate.
For graph.atlas this is the number (id) of the graph to
create.
|
mode |
For graph.star it defines the direction of the
edges, in : the edges point to the center, out :
the edges point from the center, undirected : the edges
are undirected.
For igraph.tree this parameter defines the direction of the
edges. out indicates that the edges point from the parent to
the children, in indicates that they point from the children
to their parents, while undirected creates an undirected
graph.
|
center |
For graph.star the center vertex of the graph, by
default the first vertex. |
dimvector |
A vector giving the size of the lattice in each
dimension, for graph.lattice . |
nei |
The distance within which (inclusive) the neighbors on the lattice will be connected. This parameter is not used right now. |
mutual |
Logical, if TRUE directed lattices will be mutually connected. |
circular |
Logical, if TRUE the lattice or ring will be circular. |
length |
Integer constant, for regular lattices, the size of the lattice in each dimension. |
dim |
Integer constant, the dimension of the lattice. |
children |
Integer constant, the number of children of a vertex
(except for leafs) for graph.tree . |
loops |
If TRUE also loops edges (self edges) are added. |
graph |
An object. |
el |
An edge list, a two column matrix, character or numeric. See details below. |
w |
A matrix which specifies the extended chordal ring. See details below. |
All these functions create graphs in a deterministic way.
graph.empty
is the simplest one, this creates an empty graph.
graph
creates a graph with the given edges.
graph.star
creates a star graph, in this every single vertex is
connected to the center vertex and nobody else.
graph.lattice
is a flexible function, it can create lattices of
arbitrary dimensions, periodic or unperiodic ones.
graph.ring
is actually a special case of graph.lattice
,
it creates a one dimensional circular lattice.
graph.tree
creates regular trees.
graph.full
simply creates full graphs.
graph.full.citation
creates a full citation graph. This is a
directed graph, where every i->j edge is present if and only if j<i.
If directed=FALSE
then the graph is just a full graph.
graph.atlas
creates graphs from the book An Atlas of Graphs by
Roland C. Read and Robin J. Wilson. The atlas contains all undirected
graphs with up to seven vertices, numbered from 0 up to 1252. The
graphs are listed:
graph.edgelist
creates a graph from an edge list. Its argument
is a two-column matrix, each row defines one edge. If it is
a numeric matrix then its elements are interpreted as vertex ids. If
it is a character matrix then it is interpreted as symbolic vertex
names and a vertex id will be assigned to each name, and also a
name
vertex attribute will be added.
graph.extended.chordal.ring
creates an extended chordal ring.
An extended chordal ring is regular graph, each node has the same
degree. It can be obtained from a simple ring by adding some extra
edges specified by a matrix. Let p denote the number of columns in
the ‘W
’ matrix. The extra edges of vertex i
are added according to column i mod p
in
‘W
’. The number of extra edges is the number
of rows in ‘W
’: for each row j
an edge
i->i+w[ij]
is added if i+w[ij]
is less than the number
of total nodes. See also Kotsis, G: Interconnection Topologies for
Parallel Processing Systems, PARS Mitteilungen 11, 1-6, 1993.
Every function documented here returns a graph
object.
Gabor Csardi csardi@rmki.kfki.hu
graph.adjacency
to create graphs from adjacency
matrices, graph.formula
for a handy way to create small
graphs, graph.data.frame
for an easy way to create
graphs with many edge/vertex attributes.
g1 <- graph.empty() g2 <- graph( c(1,2,2,3,3,4,5,6), directed=FALSE ) g5 <- graph.star(10, mode="out") g6 <- graph.lattice(c(5,5,5)) g7 <- graph.lattice(length=5, dim=3) g8 <- graph.ring(10) g9 <- graph.tree(10, 2) g10 <- graph.full(5, loops=TRUE) g11 <- graph.full.citation(10) g12 <- graph.atlas(sample(0:1252, 1)) el <- matrix( c("foo", "bar", "bar", "foobar"), nc=2, byrow=TRUE) g13 <- graph.edgelist(el) g15 <- graph.extended.chordal.ring(15, matrix(c(3,12,4,7,8,11), nr=2))