Fold IDs of sibship grandparents into a 2 x nInd/2 x 2 array, as they are stored in Fortran, and then stretch this into a vector that can be passed to Fortran and easily be transformed back into said 3D array.
FoldSibGPs(PedNum, Ng, Nd)pedigree, ids replaced by numbers, dummies negative.
no. genotyped indivs.
length 2 vector, no. female & male dummies.
An integer vector, with missing values as 0.