[R] Custom nonlinear self starting function w/ 2 covariates

[Sebastien Guyader]

Hello,

I'm trying to adjust a non linear model in which the biological response
variable (ratio of germinated fungus spores) is dependent on 2 covariates
(temperature and time). The response to temperature is modeled by a kind of
beta function with 2 parameters (optimal and maximum temperatures) and the
time function is a 2-parameter Weibull. Adjustments with nls or gnls work,
but I need to do mixed-effects modeling.

It seems like nlme or nlmer need self starting functions, but so far I can't
find a way to code a selfstart function with 2 "x" covariates. Is it just
impossible? Is there another way?

Thanks
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