R help - Dec 2013 - how to fit exponential curve such as a*b^t in r?

input <- "    
      t    y    
     1  5.3    
     2  7.2    
     3  9.6    
     4 12.9    
     5 17.1    
     6 23.2"         
    dat<-read.table(textConnection(input),header=TRUE,sep="")    
    t<-dat[,1]    
    y<-dat[,2]   

`y=3.975*(1.341^t)` is the resule of fit,how can i use `nls` function to get it?
	[[alternative HTML version deleted]]

On 16-12-2013, at 08:52, ???? <1248283536 at qq.com> wrote:
> input <- "    
>      t    y    
>     1  5.3    
>     2  7.2    
>     3  9.6    
>     4 12.9    
>     5 17.1    
>     6 23.2"         
>    dat<-read.table(textConnection(input),header=TRUE,sep="")
>    t<-dat[,1]    
>    y<-dat[,2]   
> 
> `y=3.975*(1.341^t)` is the resule of fit,how can i use `nls` function to
get it?

Have you looked at ?nls.
Have you simply tried

nls(y~a*b^t,data=dat)

You can also do a linear regression  on  log(y) ~ A + B* t.
And afterwards transform to the original coefficients.

Berend
> 	[[alternative HTML version deleted]]
> 
Please do not post in html.
> ______________________________________________
> R-help at r-project.org mailing list
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http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Read the examples section of

?nls

You probably need to provide a start list of values.

There are some points you should note from the Posting Guide mentioned in the
footer of emails on this list: this is not a homework help forum, you should
provide a reproducible example, and you should not post in HTML format.
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"????" <1248283536 at qq.com> wrote:
>input <- "    
>      t    y    
>     1  5.3    
>     2  7.2    
>     3  9.6    
>     4 12.9    
>     5 17.1    
>     6 23.2"         
>    dat<-read.table(textConnection(input),header=TRUE,sep="")
>    t<-dat[,1]    
>    y<-dat[,2]   
>
>`y=3.975*(1.341^t)` is the resule of fit,how can i use `nls` function
>to get it?
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.