lowerdiag2mat: Convert a vector of the lower diagonoal of a symmetrical...
In ashiklom/mvtraits: Fit multivariate models to partially missing trait data

Storing just the lower diagonal is an efficient way to store MCMC samples of a matrix (and, in fact, is how matrices are stored by the samplers in fit_mvnorm() and fit_mvnorm_hier()).

1 2	lowerdiag2mat(vec, col_names = TRUE, corr = FALSE, colorder = NULL, hier = FALSE)

`vec`	Vector of lower diagonal values
`col_names`	(Logical) If `TRUE` (default), extract row and column names from vector names formatted as `"row..column"`.
`corr`	(Logical) If `TRUE`, assume this is a correlation matrix where the diagonal is fixed at 1 and therefore not stored.
`colorder`	Optional numeric or character vector specifying the desired column order.
`hier`	(Logical) Whether the vector names also include a group name. Only used if `col_names` is `TRUE`.