Hi there,
 
The optim(par, fn, ...parscale...) function in R requires 'parscale' which is defined as:
 
"A vector of scaling values for the parameters. Optimisation is performed on 'par/parscale' and these should be comparable in the sense that a unit change in any element (??) produces a unit change in the scaled value".
 
I am just not understanding the "comparable...produces".
 
Should we compare "fn(par/parscale+1)- fn(par/parscale)" with 
"fn(parscale+1) - fn(parscale)"? 
 
With this respect, we might refer to the choice of parscale=20 in the "wild function" given in the optim R documentation if you wish.
 
Many thanks in advance for your consideration.
 
Kind regards,
Tom

 

		
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