nlraa (version 1.2)

SSpquad3: self start for plateau-quadratic function

Description

Self starter for plateau-quadratic function with (three) parameters a (intercept), b (slope), c (quadratic)

Usage

pquad3(x, a, b, c)
SSpquad3(x, a, b, c)

Value

a numeric vector of the same length as x containing parameter estimates for equation specified

quadp: vector of the same length as x using the quadratic-plateau function

Arguments

x

input vector

a

the intercept

b

the slope

c

quadratic term

Details

Reference for nonlinear regression Archontoulis and Miguez (2015) - (doi:10.2134/agronj2012.0506).

Examples

# \donttest{
require(ggplot2)
require(minpack.lm)
set.seed(123)
x <- 1:30
y <- pquad3(x, 20.5, 0.36, -0.012) + rnorm(30, 0, 0.3)
dat <- data.frame(x = x, y = y)
fit <- nlsLM(y ~ SSpquad3(x, a, b, c), data = dat)
## plot
ggplot(data = dat, aes(x = x, y = y)) + 
  geom_point() + 
  geom_line(aes(y = fitted(fit)))
# }