Hi,

Try

> d <- data.frame(samples, species)
> fit = nls(species ~ a *(1 - exp(-b*samples)), start = list(a = 27, b =
.15), data = d)
> summary(fit)

Formula: species ~ a * (1 - exp(-b * samples))

Parameters:
  Estimate Std. Error t value Pr(>|t|)
a 35.82472    3.02073  11.860 6.10e-10 ***
b  0.07168    0.01023   7.009 1.53e-06 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 1.333 on 18 degrees of freedom

Number of iterations to convergence: 5
Achieved convergence tolerance: 2.837e-06

HTH
Jorge


On Thu, Apr 28, 2011 at 4:56 PM, BornSurvivor <> wrote:

> I have the following data set, and I have to find the line of best fit
> using
> this equation,
> y = a*(1 - exp(-b*x)).
>
> samples = seq(1,20,by=1)
> species = c(5,8,9,9,11,11,12,15,17,19,20,20,21,23,23,25,25,27,27,27)
> plot(samples,species, main = "Accumulation Curve for Tree Species
> Richness",
> xlab = "Samples", ylab = "Number of Species")
> curve((y = 27*(1 - exp(-.15*x))),from=0,to=20,add = T)
>
> I tried to find the best fit curve using:
>
> fit = nls(species ~ a *(1 - exp(-b*x)),start = list(a = 27, b = .15)
>
> but I get a "parameters without starting value in 'data': x" and I don't
> have any idea what this means, or how to fix the above code.
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/Generating-a-best-fit-line-for-non-linear-data-tp3482193p3482193.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>

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