perturb_dec_fact:

Decrease factor for x-s perturbation. $\;$
The factor by which the perturbation is decreased when a trial value is deduced from the size of the most recent successful perturbation. (This is kappa_w- in the implementation paper.) The valid range for this real option is $0 < {\tt perturb\_dec\_fact } < 1$ and its default value is $0.333333$.