Pasture yield data

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Description

The Ratkowsky2 data frame has 9 rows and 2 columns.

Format

This data frame contains the following columns:

y

A numeric vector of pasture yields.

x

A numeric vector of growing times.

Details

This model and data are an example of fitting sigmoidal growth curves taken from Ratkowsky (1983). The response variable is pasture yield, and the predictor variable is growing time.

Source

Ratkowsky, D.A. (1983). Nonlinear Regression Modeling. New York, NY: Marcel Dekker, pp. 61 and 88.

Examples

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Try <- function(expr) if (!inherits(val <- try(expr), "try-error")) val
plot(y ~ x, data = Ratkowsky2)

Try(fm1 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
           start = c(b1 = 100, b2 = 1, b3 = 0.1)))
Try(fm1a <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2,
            trace = TRUE, alg = "port", 
            start = c(b1 = 100, b2 = 1, b3 = 0.1)))
Try(fm2 <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
           start = c(b1 = 75, b2 = 2.5, b3 = 0.07)))
Try(fm2a <- nls(y ~ b1 / (1+exp(b2-b3*x)), data = Ratkowsky2,
            trace = TRUE, alg = "port", 
            start = c(b1 = 75, b2 = 2.5, b3 = 0.07)))
Try(fm3 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
           start = c(b2 = 1, b3 = 0.1), alg = "plinear"))
Try(fm4 <- nls(y ~ 1 / (1+exp(b2-b3*x)), data = Ratkowsky2, trace = TRUE,
           start = c(b2 = 2.5, b3 = 0.07), alg = "plinear"))

## Using a self-starting model
Try(fm5 <- nls(y ~ SSlogis(x, Asym, xmid, scal), data = Ratkowsky2))
summary(fm5)