| 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))