## Stomatal conductance can be modeled as a simple function of
## photosynthesis and other environmental parameters
## This model is known as the Ball-Berry model

sc <- function(A, rh, Cs, int = 0.003, slope = 5.6){

  ans <- slope * (rh * A / Cs) + int

  ans

}

## Testing this function

As <- seq(0, 50)

rh <- 0.7

Cs <- 400

stomc <- sc(As, rh = rh, Cs = Cs)

xyplot(stomc ~ As,
       xlab = "Assimilation",
       ylab = "Stomatal Conductance")

xyplot(stomc ~ I(As * rh)/Cs)