One other minor glitch I just noticed:
x <- seq_along(x)
should read
x <- seq_along(y)
cheers,
Rolf
On 08/04/12 10:08, Gabor Grothendieck wrote:
On Sat, Apr 7, 2012 at 3:58 PM, Gabor Grothendieck
<ggrothendi...@gmail.com> wrote:
On Fri, Apr 6, 2012 at 9:42 PM, help ly<help.ly2...@gmail.com> wrote:
Dear All,
I would like to make a quadratic with a plateau model in R. Is there a
package in R doing this? The bentcableAR package seems won't work.
The link below describes what I am looking for in R exactly:
http://support.sas.com/documentation/cdl/en/statug/63033/HTML/default/viewer.htm#statug_nlin_sect033.htm
Use nls directly:
y<- c(0.46, 0.47, 0.57, 0.61, 0.62, 0.68, 0.69, 0.78, 0.7, 0.74,
0.77, 0.78, 0.74, 0.8, 0.8, 0.78)
x<- seq_along(x)
Mean<- function(x, alpha, beta, gamma) {
pmin(alpha + beta*x + gamma*x*x, alpha - beta^2/(4 * gamma))
}
fm<- nls(y ~ Mean(x, alpha, beta, gamma), start = list(alpha = 0.45,
beta = 0.05, gamma = -0.0025))
fm
summary(fm)
plot(y ~ x)
lines(fitted(fm) ~ x)
It was pointed out to me offline that Mean as defined above is not
identical to the definition in the poster's link. Here is a revision:
y<- c(0.46, 0.47, 0.57, 0.61, 0.62, 0.68, 0.69, 0.78, 0.7, 0.74,
0.77, 0.78, 0.74, 0.8, 0.8, 0.78)
x<- seq_along(x)
Mean<- function(x, alpha, beta, gamma) {
ifelse(x< -beta/(2 * gamma), alpha + beta*x + gamma*x*x,
alpha - beta^2/(4 * gamma))
}
fm<- nls(y ~ Mean(x, alpha, beta, gamma), start = list(alpha = 0.45,
beta = 0.05, gamma = -0.0025))
fm
summary(fm)
plot(y ~ x)
lines(fitted(fm) ~ x)
with(as.list(coef(fm)), abline(v = -beta/(2 * gamma)))
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