[R] nls.control in gnls
claus at ekstroem.dk
Thu Jul 24 10:47:15 CEST 2003
I've made a selfStart function for use with gnls and the
following piece of code works nicely:
check1 <- gnls(y ~ spot.shape.fct(xcord, ycord, background, spotintensity,
rho, sigma, delta, mux, muy),
start=getInitial(y ~ spot.shape.fct(xcord, ycord,
background, spotintensity, rho,
sigma, delta, mux, muy), data=claus),
spot.shape.fct is the selfStart function and I later want to include
a correlation term which is why I'm using gnls instead of nls. I want to
get rid of the start= option, but I keep getting the following error
Error in nls(formula = y ~ spot.shape.fct(xcord, ycord, background,
number of iterations exceeded maximum of 50
>From the help page and the glns code I can see that the initial start
values are improved by estimating the parameters in a model without the
correlation structures that are possible with gnls. This is quite
reasonable and will quite likely improve the convergence succes and time
once a correlation is introduced.
Obviously the call to nls does not converge before the standard 50
iterations specified in nls.control so I was wondering if it is possible
to pass nls.control information on to nls when calling gnls?
Several work-around exists:
* Write a better initial function to get more precise starting values,
i.e., fewer iterations needed for nls.
* Make a new function my.own.gnls where nls.control(maxiter=100) is
set in the call to nls.
Maybe it would even be a good idea to pass nlsMaxIter from gnlsControl
on to the initial call to nls? As far as I can see from the code it is
only used in maximization after the call to get the starting value.
Claus Thorn Ekstrøm <ekstrom at dina.kvl.dk>
Dept of Mathematics and Physics, KVL
DK-1871 Frederiksberg C
Phone:[+45] 3528 2341
Fax: [+45] 3528 2350
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