[R] Non linear regression with complex equation

[jeff_hawkes]

Apologies for the phrasing of the question.
I've sorted the problem (thanks Bert Gunter) by using the curly brackets {}
as below (using a simplified version of my real model). I hope this helps
someone else!

Jeff
-----------------------
> data
          Alpha         ip           X
1     0.7106967  0.3616727 0.006027879
2     2.1678517  5.0615917 0.084359861
3     4.4066250 11.2282945 0.187138242
4     9.8495694 18.0534974 0.300891624
5    27.7247098 29.2064434 0.486774057
6    70.6931430 35.3946092 0.589910153
7   133.1240255 46.0347288 0.767245480
8   214.7851844 49.3811149 0.823018582
9   359.5511036 58.5069583 0.975115972
10  748.1840127 57.3744477 0.956240795
11 2129.9844080 60.0000000 1.000000000
> c<-1.83e-9
> cFe=c
> model<-nls({Fe1<-cFe/(Alpha+1+k*c)
+ X~Alpha/(Alpha+1+k*c/(1+k*Fe1))},start=list(k=1e10))
> summary(model)

Formula: X ~ Alpha/(Alpha + 1 + k * c/(1 + k * Fe1))

Parameters:
   Estimate Std. Error t value Pr(>|t|)    
k 3.491e+10  7.190e+09   4.856 0.000665 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

Residual standard error: 0.05589 on 10 degrees of freedom

Number of iterations to convergence: 8 
Achieved convergence tolerance: 2.393e-06 


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