SSlogis {stats} | R Documentation |
This selfStart
model evaluates the logistic
function and its gradient. It has an initial
attribute that
creates initial estimates of the parameters Asym
,
xmid
, and scal
.
SSlogis(input, Asym, xmid, scal)
input |
a numeric vector of values at which to evaluate the model. |
Asym |
a numeric parameter representing the asymptote. |
xmid |
a numeric parameter representing the |
scal |
a numeric scale parameter on the |
a numeric vector of the same length as input
. It is the value of
the expression Asym/(1+exp((xmid-input)/scal))
. If all of
the arguments Asym
, xmid
, and scal
are
names of objects the gradient matrix with respect to these names is attached as
an attribute named gradient
.
JosÃ© Pinheiro and Douglas Bates
Chick.1 <- ChickWeight[ChickWeight$Chick == 1, ] SSlogis(Chick.1$Time, 368, 14, 6) # response only Asym <- 368; xmid <- 14; scal <- 6 SSlogis(Chick.1$Time, Asym, xmid, scal) # response and gradient getInitial(weight ~ SSlogis(Time, Asym, xmid, scal), data = Chick.1) ## Initial values are in fact the converged values fm1 <- nls(weight ~ SSlogis(Time, Asym, xmid, scal), data = Chick.1) summary(fm1)