Increase factor for x-s perturbation for very first perturbation.
The factor by which the perturbation is increased
when a trial value was not sufficient - this
value is used for the computation of the very
first perturbation and allows a different value
for for the first perturbation than that used for
the remaining perturbations. (This is
bar_kappa_w+ in the implementation paper.) The valid range for this real option is
and its default value is .