gompertz: Gompertz equation (Gompertz, 1825) In nlraa: Non-linear regression for agricultural applications

Description

Gompertz equation (Gompertz, 1825). This is equation 2.3 in Table 1.

Usage

 `1` ```gompertz(time, tmax, theta, Yo) ```

Arguments

 `time` a numeric vector of values at which to evaluate the model. `tmax` tmax is the time when crop growth rate is maximum and Y = Yo/exp `theta` theta determines the curvature `Yo` Yo is the max Y

Details

An alternative way to Richards equation to generate asymetric growth with less parameters Applied to describe water stress index, crop N-uptake, seed germination, crop growth, LAI development, etc. Remark at time = 0, Y is not zero

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

`SSgompertz`
 ```1 2 3 4 5 6 7 8``` ```require(lattice) ## Set parameter values and plot the relationship time <- seq(0, 150,5) ans1 <- gompertz(time, tmax = 60, theta = 0.09, Yo=100) ans2 <- gompertz(time, tmax = 60, theta = 0.07, Yo=100) ans3 <- gompertz(time, tmax = 60, theta = 0.05, Yo=100) ans4 <- gompertz(time, tmax = 60, theta = 0.03, Yo=100) xyplot(ans1 + ans2 + ans3 + ans4 ~ time, type="l", auto.key=TRUE, ylab = "text", xlab = "time") ```