chillingUnits: Chilling units

In baeyc/dormancy:

Description

Compute chilling units accumulated by a plant, according to a beta-shaped function.

Usage

chillingUnits(
  temp.data,
  var.names = list(temp = "temp", date = "date", duration = "duration"),
  temp.min = -5,
  temp.max = 15,
  mu,
  s
)

Arguments

temp.data	a data frame with the dates and temperatures to accumulate
var.names	the name of the temperature and date variables, in the format list(temp="temp.name",date="date.name",duration="duration.name")
temp.min	the threshold above which the plant is accumulating chilling units
temp.max	the threshold below which the plant is accumulating chilling units
mu	the temperature at which the plant accumulates the highest number of chilling units
s	the sample size of the underlying Beta distribution

Details

The accumulation of chilling units is expressed as the Beta law probability distribution function (pdf). The underlying Beta law is re-parametrized using the mode and the so-called sample size. More precisely, using the following definition for the pdf of the Beta law with parameters a and b:

\frac{Γ(a+b)}{Γ (a)+Γ (b)} \ x^{a-1}(1-x)^{1-b}

for 0 ≤q x ≤q 1, a>0 and b >0. Now, we further assume here that a > 1 and b > 1, so that the mode exists, and we parametrized the Beta distribution using μ and s defined as:

μ = \frac{a-1}{a+b-2}, \quad s = a+b

Since the Beta law has its support on [0,1], it is evaluated at (x-temp.min)/(temp.max-temp.min), where x is the recorded temperature, and mu is transformed into (mu-temp.min)/(temp.max-temp.min) to lie between 0 and 1

Value

a vector with the chilling units corresponding to each input temperature

baeyc/dormancy documentation built on May 7, 2021, 1:09 a.m.