

   SSasympOrig {nls}                            R Documentation

   AAssyymmppttoottiicc RReeggrreessssiioonn MMooddeell tthhrroouugghh tthhee OOrriiggiinn

   DDeessccrriippttiioonn::

        This `selfStart' model evaluates the asymptotic regres-
        sion 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.

   UUssaaggee::

        SSasympOrig(input, Asym, lrc)

   AArrgguummeennttss::

      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 loga-
             rithm of the rate constant.

   VVaalluuee::

        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'.

   AAuutthhoorr((ss))::

        Jose Pinheiro and Douglas Bates

   SSeeee AAllssoo::

        `nls', `selfStart'

   EExxaammpplleess::

        library( nls )
        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)

