diff-ergmTerm {ergm}

Difference

Description

For values of pow other than 0 , this term adds one network statistic to the model, equaling the sum, over directed edges (i,j) , of sign.action(attr[i]-attr[j])^pow if dir is "t-h" and of sign.action(attr[j]-attr[i])^pow if "h-t" . That is, the argument dir determines which vertex's attribute is subtracted from which, with tail being the origin of a directed edge and head being its destination, and bipartite networks' edges being treated as going from the first part (b1) to the second (b2).

If pow==0 , the exponentiation is replaced by the signum function: +1 if the difference is positive, 0 if there is no difference, and -1 if the difference is negative. Note that this function is applied after the sign.action . The comparison is exact, so when using calculated values of attr , ensure that values that you want to be considered equal are, in fact, equal.

Usage

# binary: diff(attr, pow=1, dir="t-h", sign.action="identity")

# valued: diff(attr, pow=1, dir="t-h", sign.action="identity", form ="sum")

Arguments

attr

a vertex attribute specification (see Specifying Vertex attributes and Levels (?nodal_attributes) for details.)

pow

exponent for the node difference

dir

determines which vertix's attribute is subtracted from which. Accepts: "t-h" (the default), "tail-head" , "b1-b2", "h-t" , "head-tail" , and "b2-b1" .

sign.action

one of "identity", "abs", "posonly", "negonly". The following sign.actions are possible:

• "identity" (the default) no transformation of the difference regardless of sign

• "abs" absolute value of the difference: equivalent to the absdiff term

• "posonly" positive differences are kept, negative differences are replaced by 0

• "negonly" negative differences are kept, positive differences are replaced by 0

form

character how to aggregate tie values in a valued ERGM

Note

this term may not be meaningful for unipartite undirected networks unless sign.action=="abs" . When used on such a network, it behaves as if all edges were directed, going from the lower-indexed vertex to the higher-indexed vertex.

See Also

ergmTerm for index of model terms currently visible to the package.

Keywords

bipartite, directed, dyad-independent, frequently-used, quantitative nodal attribute, undirected, binary, valued