[R-sig-ME] Connectedness of rows/columns of a matrix

[David Duffy]

On Wed, 11 Jul 2012, Kevin Wright wrote:

> Two questions:
> 1. Is there a method to detect if the rows/columns of a matrix are
> connected by at least one path through the matrix?
> 2. More generally, is there a measure of "connectedness" of the rows/columns?
> 3. Even more generally, what techniques do people use to diagnose
> non-estimability?

The rank of the design matrix for these kinds of problems.  For more 
elaborate SEMs, run from different start values and get different answers 
;)