nls troubles: Missing value or an infinity produced when evaluating the model

Question

I am an R newbie trying to fit plant photosynthetic light response curves (saturating, curvilinear) to a particular model accepted by experts. The goal is to get estimated c

Answer 1

minpack.lm to the rescue:

library(minpack.lm)
curve.nlslrc = nlsLM(photolrc ~ Am*(1-((1-(Rd/Am))^(1-(PARlrc/LCP)))),
                   start=list(Am=(max(photolrc)-min(photolrc)),
                              Rd=-min(photolrc),
                              LCP= (max(photolrc)-1)),
                   data = curvelrc)
coef(curve.nlslrc)
  #      Am         Rd        LCP 
  #8.011311   1.087484 -20.752957

plot(photolrc ~ PARlrc, data = curvelrc)
lines(0:1300, 
      predict(curve.nlslrc, 
              newdata = data.frame(PARlrc = 0:1300)))

If you pass start = list(Am = 8, Rd = 1, LCP = -20) to nls you also get a successful fit.

I don't know if the parameter values are sensible estimates considering the science behind this. Can LCP be negative?