Description Usage Arguments Details Value Author(s) See Also Examples
It is often useful to create a graph with given vertex degrees. This is
exactly what sample_degseq
does.
1 2 3 4 5 6 7  sample_degseq(
out.deg,
in.deg = NULL,
method = c("simple", "vl", "simple.no.multiple")
)
degseq(...)

out.deg 
Numeric vector, the sequence of degrees (for undirected
graphs) or outdegrees (for directed graphs). For undirected graphs its sum
should be even. For directed graphs its sum should be the same as the sum of

in.deg 
For directed graph, the indegree sequence. By default this is

method 
Character, the method for generating the graph. Right now the “simple”, “simple.no.multiple” and “vl” methods are implemented. 
... 
Passed to 
The “simple” method connects the outstubs of the edges (undirected graphs) or the outstubs and instubs (directed graphs) together. This way loop edges and also multiple edges may be generated. This method is not adequate if one needs to generate simple graphs with a given degree sequence. The multiple and loop edges can be deleted, but then the degree sequence is distorted and there is nothing to ensure that the graphs are sampled uniformly.
The “simple.no.multiple” method is similar to “simple”, but tries to avoid multiple and loop edges and restarts the generation from scratch if it gets stuck. It is not guaranteed to sample uniformly from the space of all possible graphs with the given sequence, but it is relatively fast and it will eventually succeed if the provided degree sequence is graphical, but there is no upper bound on the number of iterations.
The “vl” method is a more sophisticated generator. The algorithm and
the implementation was done by Fabien Viger and Matthieu Latapy. This
generator always generates undirected, connected simple graphs, it is an
error to pass the in.deg
argument to it. The algorithm relies on
first creating an initial (possibly unconnected) simple undirected graph
with the given degree sequence (if this is possible at all). Then some
rewiring is done to make the graph connected. Finally a MonteCarlo
algorithm is used to randomize the graph. The “vl” samples from the
undirected, connected simple graphs unformly.
The new graph object.
Gabor Csardi csardi.gabor@gmail.com
sample_gnp
, sample_pa
,
simplify
to get rid of the multiple and/or loops edges.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26  ## The simple generator
g < sample_degseq(rep(2,100))
degree(g)
is_simple(g) # sometimes TRUE, but can be FALSE
g2 < sample_degseq(1:10, 10:1)
degree(g2, mode="out")
degree(g2, mode="in")
## The vl generator
g3 < sample_degseq(rep(2,100), method="vl")
degree(g3)
is_simple(g3) # always TRUE
## Exponential degree distribution
## Note, that we correct the degree sequence if its sum is odd
degs < sample(1:100, 100, replace=TRUE, prob=exp(0.5*(1:100)))
if (sum(degs) %% 2 != 0) { degs[1] < degs[1] + 1 }
g4 < sample_degseq(degs, method="vl")
all(degree(g4) == degs)
## Powerlaw degree distribution
## Note, that we correct the degree sequence if its sum is odd
degs < sample(1:100, 100, replace=TRUE, prob=(1:100)^2)
if (sum(degs) %% 2 != 0) { degs[1] < degs[1] + 1 }
g5 < sample_degseq(degs, method="vl")
all(degree(g5) == degs)

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