Description Hints implemented in the ergm package

These hints may be used to control proposal probabilities.

`ergm`

package`sparse`

(dyad-independent)-
The network is sparse. This typically results in a Tie-Non-Tie (TNT) proposal regime.

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

(dyad-independent)-
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.

Specifically, 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.

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