weibull: Weibull equation (Weibull, 1951)

Description Usage Arguments Details Value Author(s) References See Also Examples

View source: R/richards.R

Description

Weibull equation (Weibull, 1951). This is equation 2.4 in Table 1 of the paper referenced below.

Usage

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weibull(time, a, b, Yo)

Arguments

time

a numeric vector of values at which to evaluate the model.

a

a and b paramaters define the shape of the response

b

a and b paramaters define the shape of the response

Yo

Yo is the max value for Y and when time is zero, Y is also zero

Details

Applied to describe water stress index, crop N-uptake, seed germination, crop growth, LAI development, etc. Remark: a and b paramaters have not direct biological interperation and the unit of paramater a depends on paramater b and therefore is difficult to provide initial estimates for non-linear regression analysis. Usually the initial paramaters were provided by trial and error. But see SSweibull.

Value

a numeric vector of length equal to the inputs

Author(s)

Fernando E. Miguez

References

Nonlinear Regression Models and Applications in Agricultural Research. Sotirios V. Archontoulis and Fernando E. Miguez. Agronomy Journal. doi: 10.2134/agronj2012.0506

See Also

SSweibull

Examples

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require(lattice)
## Set parameter values and plot the relationship
time <- seq(0, 200,5)
ans1 <- weibull(time, a = 0.00025, b = 0.5, Yo=100)
ans2 <- weibull(time, a = 0.00025, b = 1.5, Yo=100)
ans3 <- weibull(time, a = 0.00025, b = 2, Yo=100)
ans4 <- weibull(time, a = 0.00025, b = 3, Yo=100)
xyplot(ans1  + ans2 + ans3 + ans4 ~ time, type="l", auto.key=TRUE, ylab = "text", xlab = "time")

nlraa documentation built on May 31, 2017, 2:50 a.m.