R help - Oct 2003 - NLS estimation: Starting values

Dear All,

I am trying to fit to the data a nonlinear function, say z(tau;b) where tau 
is the independent variable and b is 3x1 vector of parameters. Following 
previous suggestions from the list, I am trying to find some "optimal"
starting values for the three parameters by using the command 'optim'
and
then feed these values to nls for estimation. Does anybody know hot to use 
'optim' for this purpose?

Many thanks,
Giovanni

optim() needs starting values too, but *may* be more robust than nls to 
their specification ....

On Fri, 24 Oct 2003, Giovanni Caggiano wrote:
> I am trying to fit to the data a nonlinear function, say z(tau;b) where tau
> is the independent variable and b is 3x1 vector of parameters. Following 
> previous suggestions from the list, I am trying to find some
"optimal"
> starting values for the three parameters by using the command
'optim' and
> then feed these values to nls for estimation. Does anybody know hot to use 
> 'optim' for this purpose?
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595