From a sparse matrix object, the three column, row ordered lower triangle of
non-zero elements is created. Mostly used within other functions (i.e.,
makeD)
sm2list(A, rownames = NULL, colnames = c("row", "column", "A"))a sparse matrix
a list of rownames from the 'A' matrix.
the columns will be labeled however they are entered in this character vector
returns the list form of the sparse matrix as a data.frame
The sparse matrix and three column format must fit CERTAIN assumptions about row/column sorting and lower/upper triangle matrix.
Adapted from a function in the MCMCglmm package