nlraa (version 0.98)

SSpexpf: self start for plateau-exponential function

Description

Self starter for an plateau-exponential function

Usage

pexpf(x, a, xs, c)
SSpexpf(x, a, xs, c)

Arguments

x

input vector (x)

a

represents the value for the plateau

xs

represents the breakpoint at which the plateau ends

c

represents the exponential rate

Value

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

pexpf: vector of the same length as x using the pexpf function

Details

The equation is: \(for x < xs: y = a and x >= xs: a * exp(c * (x-xs))\).

Examples

# NOT RUN {
require(ggplot2)
set.seed(1234)
x <- 1:30
y <- pexpf(x, 20, 15, -0.2) + rnorm(30, 0, 1)
dat <- data.frame(x = x, y = y)
fit <- nls(y ~ SSpexpf(x, a, xs, c), data = dat)
## plot
ggplot(data = dat, aes(x = x, y = y)) + 
  geom_point() + 
  geom_line(aes(y = fitted(fit)))
# }