R help - Sep 2005 - control parameter for Nelder-Mead algorithm in optim()

Hi,

In manual for optim() function, there are three control parameters for 
Nelder-Mead algorithm: alpha (reflection),beta(contraction) and 
gamma(expansion), but in the original paper, there is another parameter 
delta which controls shrinkage, how can I set this shrink parameter? Or is 
beta actually the same meaning as delta?

TIA

WC