37 lines
1.0 KiB
Plaintext
37 lines
1.0 KiB
Plaintext
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\name{D1tr}
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\alias{D1tr}
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\title{Numerical Derivatives of (x,y) Data}
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\description{
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Compute the numerical derivatives of \eqn{f()} given
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observations \code{(x[i], y ~= f(x[i]))}.
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\code{D1tr} is the \emph{\bold{tr}ivial} discrete first derivative
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using simple difference ratios.
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This is \bold{far} from optimal and only kept here for reference.
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}
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\usage{
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D1tr(y, x = 1)
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}
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\arguments{
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\item{x,y}{numeric vectors of same length, supposedly from a model
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\code{y ~ f(x)}. For \code{D1tr()}, \code{x} can have length one
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and then gets the meaning of \eqn{h = \Delta x}.}
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}
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\value{
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\code{D1tr()} returns a numeric vector of the length of \code{y}.
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}
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\author{Martin Maechler, in 1992 (for S).}
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\seealso{\code{\link[sfsmisc]{D1D2}} which directly uses the 2nd
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derivative of the smoothing spline; \code{\link{smooth.spline}}.
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}
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\examples{
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set.seed(330)
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x <- sort(runif(500, 0,10))
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y <- sin(x) + rnorm(500)/100
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f1 <- D1tr(x=x,y=y)
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plot(x,f1, ylim = range(c(-1,1, f1)))
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curve(cos(x), col=3, add= TRUE)
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}
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\keyword{smooth}
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