felm.diammatrix(flist, approx=TRUE)length(flist).flist defines a bipartite
graph in which the vertices are the levels of the factors, and two
vertices are adjacent if they are observed simultaneously. The
connected components of this graph
are important for identification of the coefficients for the factor
levels, i.e. for getfe. But experience and some trials have led
the author to speculate that the diameter of the graph (or its largest
component) is also important for the convergence rate. Specifically,
the author suspects that under some assumptions, time to convergence
goes like the square of the diameter. At least in the case of two
factors.
This function computes the diameter for each pair of factors. If the
graph is disconnected, the largest connected component is used. If
accel=TRUE (the default), the diameter is approximated from
below by drawing two sets of 10 random vertices and finding the
maximum length of the shortest paths between them.