Generation of random graphs based on different vertex types.

## Usage

```
sample_pref(
nodes,
types,
type.dist = rep(1, types),
fixed.sizes = FALSE,
pref.matrix = matrix(1, types, types),
directed = FALSE,
loops = FALSE
)
pref(...)
sample_asym_pref(
nodes,
types,
type.dist.matrix = matrix(1, types, types),
pref.matrix = matrix(1, types, types),
loops = FALSE
)
asym_pref(...)
```

## Arguments

- nodes
The number of vertices in the graphs.

- types
The number of different vertex types.

- type.dist
The distribution of the vertex types, a numeric vector of length ‘types’ containing non-negative numbers. The vector will be normed to obtain probabilities.

- fixed.sizes
Fix the number of vertices with a given vertex type label. The

`type.dist`

argument gives the group sizes (i.e. number of vertices with the different labels) in this case.- pref.matrix
A square matrix giving the preferences of the vertex types. The matrix has ‘types’ rows and columns. When generating an undirected graph, it must be symmetric.

- directed
Logical constant, whether to create a directed graph.

- loops
Logical constant, whether self-loops are allowed in the graph.

- ...
Passed to the constructor,

`sample_pref()`

or`sample_asym_pref()`

.- type.dist.matrix
The joint distribution of the in- and out-vertex types.

## Details

Both models generate random graphs with given vertex types. For
`sample_pref()`

the probability that two vertices will be connected
depends on their type and is given by the ‘pref.matrix’ argument.
This matrix should be symmetric to make sense but this is not checked. The
distribution of the different vertex types is given by the
‘type.dist’ vector.

For `sample_asym_pref()`

each vertex has an in-type and an
out-type and a directed graph is created. The probability that a directed
edge is realized from a vertex with a given out-type to a vertex with a
given in-type is given in the ‘pref.matrix’ argument, which can be
asymmetric. The joint distribution for the in- and out-types is given in the
‘type.dist.matrix’ argument.

The types of the generated vertices can be retrieved from the
`type`

vertex attribute for `sample_pref()`

and from the
`intype`

and `outtype`

vertex attribute for `sample_asym_pref()`

.

## See also

Random graph models (games)
`erdos.renyi.game()`

,
`sample_()`

,
`sample_bipartite()`

,
`sample_correlated_gnp()`

,
`sample_correlated_gnp_pair()`

,
`sample_degseq()`

,
`sample_dot_product()`

,
`sample_fitness()`

,
`sample_fitness_pl()`

,
`sample_forestfire()`

,
`sample_gnm()`

,
`sample_gnp()`

,
`sample_grg()`

,
`sample_growing()`

,
`sample_hierarchical_sbm()`

,
`sample_islands()`

,
`sample_k_regular()`

,
`sample_last_cit()`

,
`sample_pa()`

,
`sample_pa_age()`

,
`sample_sbm()`

,
`sample_smallworld()`

,
`sample_traits_callaway()`

,
`sample_tree()`

## Author

Tamas Nepusz ntamas@gmail.com and Gabor Csardi csardi.gabor@gmail.com for the R interface

## Examples

```
pf <- matrix(c(1, 0, 0, 1), nrow = 2)
g <- sample_pref(20, 2, pref.matrix = pf)
if (FALSE) { # rlang::is_installed("tcltk") && rlang::is_interactive()
# example code
tkplot(g, layout = layout_with_fr)
}
pf <- matrix(c(0, 1, 0, 0), nrow = 2)
g <- sample_asym_pref(20, 2, pref.matrix = pf)
if (FALSE) { # rlang::is_installed("tcltk") && rlang::is_interactive()
tkplot(g, layout = layout_in_circle)
}
```