FitDoubleLogGu: Fit a double logistic equation to a vector according to Gu et al. (2003)

Description

This function fits a double logistic curve to observed values using the function as described in Gu et al. (2003).

Usage

FitDoubleLogGu(x, t = index(x), tout = t, hessian=FALSE, 
sf=quantile(x, probs=c(0.05, 0.95), na.rm=TRUE), ...)

Value

A list containing the following items.

predicted: Predicted values from the equation
params: Equation parameters
formula: The equation

Arguments

x: A vector or, better, an univariate ts or zoo object.
t: A vector of time (in numeric doys), if not provided index(x) is retrieved.
tout: For gapfilling pourposes, a vector of time steps at which the function can be predicted.
hessian: Currently unimplemented.
sf: Scaling factors required to normalize the data prior to the fitting. If the function is called by e.g. greenProcess sf is automatically calculated.
...: Further arguments currenlty unused.

Author

Gianluca Filippa <gian.filippa@gmail.com>

Details

The function estimates parameters of the double logistic equation from Gu et al. 2003. The wrapper function GuFit calls this function and additionally allows the calculation of uncertainty. So better use GuFit.

References

Gu L, Post WM, Baldocchi D, Black TA, Suyker AE, Verma SB, Vesala T, Wofsy SC. (2009) Characterizing the Seasonal Dynamics of Plant Community Photosynthesis Across a Range of Vegetation Types. In: Phenology of Ecosystem Processes (Ed: Noormets A, Springer New York), pp 35-58.