# 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") ```