SSlogis
SelfStarting Nls Logistic Model
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
.
 Keywords
 models
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 ofSSlogis
will beAsym/2
atxmid
.  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((xmidinput)/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
.
See Also
Examples
library(stats)
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