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% File src/library/grDevices/man/chull.Rd
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% File src/library/grDevices/man/chull.Rd
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% Part of the R package, http://www.R-project.org
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% Part of the R package, http://www.R-project.org
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% Copyright 1995-2007 R Core Team
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% Copyright 1995-2013 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{chull}
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\name{chull}
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\alias{chull}
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\alias{chull}
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\title{Compute Convex Hull of a Set of Points}
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\title{Compute Convex Hull of a Set of Points}
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  set of points specified.
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  set of points specified.
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}
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}
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\details{
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\details{
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  \code{\link{xy.coords}} is used to interpret the
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  \code{\link{xy.coords}} is used to interpret the
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  specification of the points. The algorithm is that given by Eddy (1977).
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  specification of the points. The algorithm is that given by Eddy (1977).
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  \sQuote{Peeling} as used in the S function \code{chull} can be
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  implemented by calling \code{chull} recursively.
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}
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}
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\value{
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\value{
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  An integer vector giving the indices of the points lying on the
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  An integer vector giving the indices of the unique points lying on the
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  convex hull, in clockwise order.
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  convex hull, in clockwise order.  (The first will be returned for
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  duplicate points.)
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}
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}
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\references{
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\references{
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  \emph{The New S Language}.
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  \emph{The New S Language}.
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  Wadsworth & Brooks/Cole.
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  Wadsworth & Brooks/Cole.
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    Mathematical Software}, \bold{3}, 411--412.
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    Mathematical Software}, \bold{3}, 411--412.
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}
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}
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\seealso{\code{\link{xy.coords}}, \code{\link{polygon}}}
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\seealso{\code{\link{xy.coords}}, \code{\link{polygon}}}
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\examples{
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\examples{
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require(stats)
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X <- matrix(rnorm(2000), ncol = 2)
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X <- matrix(stats::rnorm(2000), ncol = 2)
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chull(X)
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chull(X)
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\dontrun{
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\dontrun{
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  # Example usage from graphics package
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  # Example usage from graphics package
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  plot(X, cex = 0.5)
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  plot(X, cex = 0.5)
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  hpts <- chull(X)
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  hpts <- chull(X)