inst/non_lin_models/Mod_epm1.R

In txm676/mmSAR2: Fit and Compare Species-Area Relationship Models Using Multimodel Inference

# EXTENDED POWER MODEL 1 (TJORVE 2009)
model <- list(
  name = c("Extended Power model 1"),
  formula = expression(S==c*A^(z*A^-d)),
  exp = expression(c*A^(z*A^-d)),
  shape = "convex/sigmoid",
  asymp = function(pars)FALSE,
  parLim  =  c("Rplus","R","R"),
  custStart = function(data)c(5,.25,.15),
  #initials values function
  init = function(data){
    if(any(data$S==0)){
    log.data=data.frame(A=log(data$A),S=log(data$S+.5))
    }else{log.data=log(data)}
    res=stats::lm(S~A,log.data)$coefficients
    res=c(exp(res[1]),res[2],.15)
    names(res)=model$parNames
    return(res)}
)