FitDoubleLogGu {phenopix}

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), ...)

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.

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.

Value

A list containing the following items.

predicted

Predicted values from the equation

params

Equation parameters

formula

The equation

Author(s)

Gianluca Filippa <[e-mail]>

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.