# R/SScousens85.R In OnofriAndreaPG/aomisc: Statistical methods for the agricultural sciences

#### Defines functions cousens85.fun

```#Yield - Weed Density function ###################
cousens85.fun <- function(Dens, Ywf, i, A) {
Ywf*(1 - (i * Dens) / (100 * (1 + i * Dens/A)))
}

"DRC.cousens85" <-
function(fixed = c(NA, NA, NA), names = c("YWF", "i", "a"))
{
## Checking arguments
numParm <- 3
if (!is.character(names) | !(length(names) == numParm)) {stop("Not correct 'names' argument")}
if (!(length(fixed) == numParm)) {stop("Not correct 'fixed' argument")}

## Fixing parameters (using argument 'fixed')
notFixed <- is.na(fixed)
parmVec <- rep(0, numParm)
parmVec[!notFixed] <- fixed[!notFixed]

## Defining the non-linear function
fct <- function(x, parm)
{
parmMat <- matrix(parmVec, nrow(parm), numParm, byrow = TRUE)
parmMat[, notFixed] <- parm

YWF <- parmMat[, 1]; i <- parmMat[, 2]; a <- parmMat[, 3]
YWF*(1 - (i*x) / (100 * (1 + i * x/a)))
}

## Defining self starter function
ssfct <- function(dataf)
{
x <- dataf[, 1]
y <- dataf[, 2]

YWF <- max(y)+10e-06
YL <- (1 - y/YWF)*100
#regression on pseudo y values
pseudoY <- 1 /  (YL + 0.000001)
pseudoX <- 1 / (x + 0.00001)
coefs <- coef( lm(pseudoY ~ pseudoX) )
a <- 1 / coefs[1]; i <- 1 / coefs[2]

return(c(YWF, i, a)[notFixed])
}

## Defining names
pnames <- names[notFixed]

## Defining derivatives

## Defining the ED function

## Defining the inverse function

## Defining descriptive text
text <- "Yield-Weed Density function (Cousens, 1985)"

## Returning the function with self starter and names
returnList <- list(fct = fct, ssfct = ssfct, names = pnames, text = text, noParm = sum(is.na(fixed)))

class(returnList) <- "drcMean"
invisible(returnList)
}
```
OnofriAndreaPG/aomisc documentation built on Feb. 26, 2024, 8:21 p.m.