self start for plateau-quadratic function
Self starter for plateau-quadratic function with (three) parameters a (intercept), b (slope), c (quadratic)
pquad3(x, a, b, c) SSpquad3(x, a, b, c)
x |
input vector |
a |
the intercept |
b |
the slope |
c |
quadratic term |
Reference for nonlinear regression Archontoulis and Miguez (2015) - (doi:10.2134/agronj2012.0506).
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
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)))
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