\HeaderA{NLSstClosestX}{Inverse Interpolation}{NLSstClosestX}
\methaliasA{NLSstClosestX.sortedXyData}{NLSstClosestX}{NLSstClosestX.sortedXyData}
\keyword{manip}{NLSstClosestX}
\begin{Description}\relax
Use inverse linear interpolation to approximate the \code{x} value at
which the function represented by \code{xy} is equal to \code{yval}.
\end{Description}
\begin{Usage}
\begin{verbatim}
NLSstClosestX(xy, yval)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{xy}] a \code{sortedXyData} object
\item[\code{yval}] a numeric value on the \code{y} scale
\end{ldescription}
\end{Arguments}
\begin{Value}
A single numeric value on the \code{x} scale.
\end{Value}
\begin{Author}\relax
Jose Pinheiro and Douglas Bates
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{sortedXyData}{sortedXyData}}, \code{\LinkA{NLSstLfAsymptote}{NLSstLfAsymptote}},
\code{\LinkA{NLSstRtAsymptote}{NLSstRtAsymptote}}, \code{\LinkA{selfStart}{selfStart}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
DNase.2 <- DNase[ DNase$Run == "2", ]
DN.srt <- sortedXyData( expression(log(conc)), expression(density), DNase.2 )
NLSstClosestX( DN.srt, 1.0 )
\end{ExampleCode}
\end{Examples}

