Covariates for row effects

[BertvanderVeen]

Wishlist: allow row.eff to also include covariates (with/without random slopes?) for which effects are assumed to be the same for all species. This allows to fit models that answer questions both with respect to the total abundance or richness at a site, as well as for species/communities. E.g.,:

gllvm(y, X, row.eff = ~elevation + (1|area), formula = ~ shrubs, num.lv = 2)