SSasympOrig               package:nls               R Documentation

Asymptotic Regression Model through the Origin

Description:

     This `selfStart' model evaluates the asymptotic regression
     function through the origin and its gradient.  It has an `initial'
     attribute that will evaluate initial estimates of the parameters
     `Asym' and `lrc' for a given set of data.

Usage:

     SSasympOrig(input, Asym, lrc)

Arguments:

   input: a numeric vector of values at which to evaluate the model.

    Asym: a numeric parameter representing the horizontal asymptote.

     lrc: a numeric parameter representing the natural logarithm of the
          rate constant.

Value:

     a numeric vector of the same length as `input'.  It is the value
     of the expression `Asym*(1 - exp(-exp(lrc)*input))'.  If all of
     the arguments `Asym' and `lrc' are names of objects, the gradient
     matrix with respect to these names is attached as an attribute
     named `gradient'.

Author(s):

     Jose Pinheiro and Douglas Bates

See Also:

     `nls', `selfStart'

Examples:

     data( Loblolly )
     Lob.329 <- Loblolly[ Loblolly$Seed == "329", ]
     SSasympOrig( Lob.329$age, 100, -3.2 )  # response only
     Asym <- 100; lrc <- -3.2
     SSasympOrig( Lob.329$age, Asym, lrc ) # response and gradient
     getInitial(height ~ SSasympOrig(age, Asym, lrc), data = Lob.329)
     ## Initial values are in fact the converged values
     fm1 <- nls(height ~ SSasympOrig( age, Asym, lrc), data = Lob.329)
     summary(fm1)

