self start for quadratic-plateau function
Self starter for quadratic plateau function with parameters a (intercept), b (slope), c (quadratic), xs (break-point)
quadp(x, a, b, c, xs) SSquadp(x, a, b, c, xs)
x |
input vector |
a |
the intercept |
b |
the slope |
c |
quadratic term |
xs |
break point of transition between quadratic and plateau |
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) set.seed(123) x <- 1:30 y <- quadp(x, 5, 1.7, -0.04, 20) + rnorm(30, 0, 0.6) dat <- data.frame(x = x, y = y) fit <- nls(y ~ SSquadp(x, a, b, c, xs), data = dat, algorithm = "port") ## plot ggplot(data = dat, aes(x = x, y = y)) + geom_point() + geom_line(aes(y = fitted(fit)))
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