optimize_costs_given_shift_position.OU.specialCase minimize the sum of
costs when the shift position is fixed.
optimize_costs_given_shift_position.OU.specialCase(phylo, conditional_law_X,
selection.strength, shifts_edges, ...)a phylogenetic tree
moments of the conditional law of X given Y, result
of function compute_M.OU.specialCase
the selection strength
the vector of the position of the shifts on the tree
List containing : beta_0 : the optimal value at the root shifts : list containing the computed tau and delta costs : vector of costs
This function find the regimes of each node using function
allocate_regimes_from_shifts and optimize the sum of costs, computed
using function compute_diff_exp.OU, in the values of the optimal values
betas (using a close formula). It then goes back to a shift expression of the
problem using function compute_shifts_from_betas.