Message-ID: <49AB9BC9.6090703@statistik.tu-dortmund.de>
Date: 2009-03-02T08:41:45Z
From: Uwe Ligges
Subject: nls does not accept start values
In-Reply-To: <OF1D96A50A.67EE108C-ONC125756D.002957D5-C125756D.0029D674@precheza.cz>
Petr PIKAL wrote:
> Hi to all
>
> OK as I did not get any response and I really need some insight I try
> again with different subject line
>
> I have troubles with correct evaluating/structure of nls input
>
> Here is an example
>
> # data
> x <-1:10
> y <-1/(.5-x)+rnorm(10)/100
>
> # formula list
> form <- structure(list(a = list(quote(y ~ 1/(a - x)), "list(a=mean(y))")),
> .Names = "a")
>
> # This gives me an error due to not suitable default starting value
>
> fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y))
>
> # This works and gives me a result
>
> fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=list(a=mean(y)))
>
> *** How to organise list "form" and call to nls to enable to use other
> then default starting values***.
>
> I thought about something like
>
> fit <- nls(form [[1]] [[1]], data.frame(x=x, y=y), start=get(form [[1]]
> [[2]]))
> ^^^^^^^^^^^^^^^^^^^
> but this gives me an error so it is not correct syntax. (BTW I tried eval,
> assign, sustitute, evalq and maybe some other options but did not get it
> right.
>
> I know I can put starting values interactively but what if I want them
> computed by some easy way which is specified by second part of a list,
> like in above example.
If you really want to orgnize it that way, why not simpler as in:
form <- list(y ~ 1/(a - x), a = mean(y))
fit <- nls(form[[1]], data.frame(x=x, y=y), start = form[2])
Uwe Ligges
> If it matters
> WXP, R2.9.0 devel.
>
> Regards
> Petr
>
> petr.pikal at precheza.cz
>
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