SSlogis: Self-Starting Nls Logistic Model
Description
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
.
Usage
SSlogis(input, Asym, xmid, scal)
Arguments
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 x
value at the
inflection point of the curve. The value of SSlogis
will be
Asym/2
at xmid
.
scal
a numeric scale parameter on the input
axis.
Value
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
.