SSRichards {NRAIA} | R Documentation |
This selfStart
model evaluates the Richards growth model
function and its gradient. It has an initial
attribute that
creates initial estimates of the parameters Asym
,
xmid
, scal
and lpow
.
SSRichards(input, Asym, xmid, scal, lpow)
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. |
lpow |
the natural logarithm of the inverse of the power to which the denominator is raised. |
a numeric vector of the same length as input
. It is the value of
the expression Asym*(1+exp((xmid-input)/scal))^(-exp(-lpow))
.
If all of the arguments Asym
, xmid
, scal
and
lpow
are names of objects, the gradient matrix with respect to
these names is attached as an attribute named gradient
.
summary(fm1 <- nls(Length ~ SSRichards(Time, Asym, xmid, scal, lpow), Leaves))