update.compute_betas_from_shifts
computes the optimal value at a daughter node,
knowing the optimal value at the parent node and the vector of shifts.
update.compute_betas_from_shifts(edgeNbr, ancestral, shifts, ...)
Updated matrix of size (Nnode + ntaxa)x1.
: Number of the edge considered
: Computed vector for the parental node
position and values of the shifts
This function is used in function compute_betas_from_shifts
and is designed to
furnish function recursionDown
with the right structure of data.