[R] reference on graph theory

Dear r users, does anyone have a suggestion of a book on graph theory, which may help designing the analysis of neuroimaging resting-states data? Thanks, Guilherme [[alternative HTML version deleted]] _

[R] sem & psych

Dear R users, I am trying to simulate some multitrait-multimethod models using the packages sem and psych but whatever I do to deal with models which do not converge I always get stuck and get error messages such as these: "Error in summary.sem(M1) : coefficient covariances cannot be computed