zwietering_gamma: Zwietering gamma model
Description
Gamma model as defined by Zwietering et al. (1992). To avoid unreasonable predictions,
it has been modified setting gamma=0 for values of x outside [xmin, xopt]
Usage
zwietering_gamma(x, xmin, xopt, n)
Arguments
x
Value of the environmental factor.
xmin
Minimum value of the environmental factor for growth.
n
Exponent of the secondary model
Value
The corresponding gamma factor.