self start for Ricker Function
Self starter for Ricker function with parameters a and b
ricker(time, a, b) SSricker(time, a, b)
time |
input vector (x) which is normally ‘time’, the smallest value should be close to zero. |
a |
which is related to the initial growth slope |
b |
which is related to the slowing down or decline |
This function is described in Archontoulis and Miguez (2015) - (doi:10.2134/agronj2012.0506) and originally in Ricker, W. E. (1954) Stock and Recruitment Journal of the Fisheries Research Board of Canada, 11(5): 559–623. (doi:10.1139/f54-039). The equation is: a * time * exp(-b * time).
a numeric vector of the same length as x (time) containing parameter estimates for equation specified
ricker: vector of the same length as x (time) using the ricker function
require(ggplot2) set.seed(123) x <- 1:30 y <- 30 * x * exp(-0.3 * x) + rnorm(30, 0, 0.25) dat <- data.frame(x = x, y = y) fit <- nls(y ~ SSricker(x, a, b), data = dat) ## plot ggplot(data = dat, aes(x = x, y = y)) + geom_point() + geom_line(aes(y = fitted(fit)))
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