SSL {statforbiology} | R Documentation |
Logistic equations
Description
These functions provide the logistic equations with 4 (L4.fun), 3 (L3.fun)
and 2 (L2.fun) parameters with self-starter for the nls
function (NLS.L4, NLS.L3 and NLS.L2) and the self-starter for logistic
function with two parameters for the drm
function in the
drc package (DRC.L2).
Usage
L4.fun(predictor, b, c, d, e)
L3.fun(predictor, b, d, e)
L2.fun(predictor, b, e)
NLS.L4(predictor, b, c, d, e)
NLS.L3(predictor, b, d, e)
NLS.L2(predictor, b, e)
DRC.L2(upper = 1, fixed = c(NA, NA), names = c("b", "e"))
Arguments
predictor |
a numeric vector of values at which to evaluate the model |
b |
model parameter (slope at inflection point) |
c |
model parameter (lower asymptote) |
d |
model parameter (higher asymptote) |
e |
model parameter (abscissa at inflection point) |
upper |
numeric. For L.2, a upper asymptote different from 1 can be specified. |
fixed |
numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed. |
names |
names. A vector of character strings giving the names of the parameters. The default is reasonable. |
Details
The logistic equation is parameterised as:
f(x) = c + \frac{d - c}{1+exp\left[-b(x - e)\right]}
for the 3- and 2-parameter model c is equal to 0, while for the 2-parameter model d is equal to 1.
Value
L4.fun, L3.fun, L2.fun, NLS.L4, NLS.L3 and NLS.L2 return a numeric value, while DRC.L2 returns a list containing the nonlinear function, the self starter function and the parameter names.
Author(s)
Andrea Onofri
Examples
data(beetGrowth)
mod3 <- nls(weightInf ~ NLS.L3(DAE, b, c, d), data = beetGrowth)
mod3b <- drm(weightInf ~ DAE, fct=DRC.L2(upper = 25), data = beetGrowth)