self start for a bell-shaped curve
Self starter for a type of bell-shaped curve
bell(x, ymax, a, b, xc) SSbell(x, ymax, a, b, xc)
x |
input vector |
ymax |
maximum value of y |
a |
parameter controlling the spread (associated with a quadratic term) |
b |
parameter controlling the spread (associated with a cubic term) |
xc |
centering parameter |
This function is described in Archontoulis and Miguez (2015) - (doi:10.2134/agronj2012.0506). One example application is Hammer et al. (2009) (doi:10.2135/cropsci2008.03.0152).
a numeric vector of the same length as x containing parameter estimates for equation specified
bell: vector of the same length as x using a bell-shaped curve
require(ggplot2) set.seed(1234) x <- 1:20 y <- bell(x, 8, -0.0314, 0.000317, 13) + rnorm(length(x), 0, 0.5) dat <- data.frame(x = x, y = y) fit <- nls(y ~ SSbell(x, ymax, a, b, xc), data = dat) ## plot ggplot(data = dat, aes(x = x, y = y)) + geom_point() + geom_line(aes(y = fitted(fit)))
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