strat-ergmHint | R Documentation |

Proposed toggles are stratified according to mixing type on a vertex attribute.

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

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 vertex 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.

`ergmHint`

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

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