Von Bertalanffy function


The von Bertalanffy growth function, or von Bertalanffy curve, is a type of growth curve model for a time series and is named after Ludwig von Bertalanffy. It is a special case of the generalised logistic function. The growth curve is used to model mean length from age in animals. The function is commonly applied in ecology to model fish growth.
The model can be written as the following:
where is age, is the growth coefficient, is a value used to calculate size when age is zero, and is asymptotic size. It is the solution of the following linear differential equation:

Seasonally-adjusted von Bertalanffy

The seasonally-adjusted von Bertalanffy is an extension of this function that accounts for organism growth that occurs seasonally. It was created by I. F. Somer in 1988.