[R] nls

[Douglas Bates]

"kjetil brinchmann halvorsen" <kjetil at entelnet.bo> writes:

> On 16 Jan 2003 at 22:15, Yan Yu wrote:
> 
> > HI,
> > i have some prob when i try to use nls().
> > my data is 1D vector, I tried to use a polynomial function(order is 3) to
> > fit it.
> > the data series is stored in x.
> > the a0, a1, a2, a3 below is coefficient, which i  hope i can get from
> > calls "nls"
> > 
> > > z <-  nls(  ~ a0 + a1 * x + a2 * x * x + a3 * x * x * x, data = x )
> 
> You haven't given a response in the formula? nls could possibly give 
> a more informative error message.

and you didn't give starting estimates for the parameters and the
model should not be fit with nls in the first place.  A polynomial in
x is a linear model in the coefficients a0, a1, a2, and a3 and should
be fit with lm, not nls.