[R] nls number of explantory variables

Christoph Buser buser at stat.math.ethz.ch
Mon Mar 13 09:14:03 CET 2006

Hi Harsh

As indicated in the answer to your first post, it is not so easy
to debug code without the code itself.

1) Have you checked the names of your variables so that you are
   sure that they are correct. For example undesired white space
   due to the automatic creation of variable names with paste()
   results in undesired variable names:

dat <- data.frame(x1 = rnorm(10), "x 2" = rnorm(10), y = rnorm(10))
nls(y ~ beta*x1  + gamma*x2 , data = dat, start = list(beta = 1, gamma = 1))
## variable name "x 2" has been changed to "x.2"

2) If you believe that nls can not handle a certain amount of
   variables you can check it easily by yourself. E.g. If your
   code works for  the variables x1,x2,...,x170, replace one
   variable by variable x181 and check if it works.
   If it does not work it is not the amount of variables.

In general (also as an answer to your first post: "Non-linear
Regression : Error in eval(expr, envir, enclos)", I would
recommend to do some debugging by starting with code that works
and go stepwise until some errors occurs. If there is a conflict
between two or more variables or a problem with over
parameterization you have a better chance to find it.



Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C13
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-44-632-4673		fax: 632-1228

Cal Stats writes:
 > Hi..
 >      is there a limit on the number of explanatory variables in nls ?
 >   i have a dataframe with the columns names x1,x2..,x300
 >   when i run nls it gives the error: " x181 not found"
 >   thought it does run when i have x1,x2,...,x170 variables.
 >   Thanks
 >   Harsh
 > ---------------------------------
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