R: Stratified dyads

strat-ergmHint {ergm} | R Documentation

## Stratified dyads

### Description

The dyads in the network are stratified according to an attribute combination. This typically results in stratifying proposals by mixing type on a vertex attribute.

### Usage

    # strat(attr=NULL, pmat=NULL, empirical=FALSE)

### Details

The user may pass a vertex attribute `attr` as an argument (the default for `attr` gives every vertex the same attribute value), and may also pass a matrix of weights `pmat` (the default for `pmat` gives equal weight to each mixing type). See Specifying Vertex Attributes and Levels for details on specifying vertex attributes. The matrix `pmat` , if specified, must have the same dimensions as a mixing matrix for the network and attribute under consideration, and the correspondence between rows and columns of `pmat` and values of `attr` is the same as for a mixing matrix.

The interpretation is that `pmat[i,j]/sum(pmat)` is the probability of proposing a toggle for mixing type `(i,j)` . (For undirected, unipartite networks, `pmat` is first symmetrized, and then entries below the diagonal are set to zero. Only entries on or above the diagonal of the symmetrized `pmat` are considered when making proposals. This accounts for the convention that mixing is undirected in an undirected, unipartite network: a tail of type `i` and a head of type `j` has the same mixing type as a tail of type `j` and a head of type `i` .)

As an alternative way of specifying `pmat` , the user may pass `empirical=TRUE` to use the mixing matrix of the network beginning the MCMC chain as `pmat` . In order for this to work, that network should have a reasonable (in particular, nonempty) edge set.

While some mixing types may be assigned zero proposal probability (either with a direct specification of `pmat` or with `empirical=TRUE` ), this will not be recognized as a constraint by all components of `ergm` , and should be used with caution.

### See Also

`ergmHint` for index of constraints and hints currently visible to the package.

[Package ergm version 4.2.1 Index]