\name{pairdist.pp3}
\alias{pairdist.pp3}
\title{Pairwise distances in Three Dimensions}
\description{
  Computes the matrix of distances between all pairs of points
  in a three-dimensional point pattern.
}
\usage{
  \method{pairdist}{pp3}(X, \dots, periodic=FALSE, squared=FALSE)
}
\arguments{
  \item{X}{
    A point pattern (object of class \code{"pp3"}).
  }
  \item{\dots}{
    Ignored.
  }
  \item{periodic}{
    Logical. Specifies whether to apply a periodic edge correction.
  }
  \item{squared}{
    Logical. If \code{squared=TRUE}, the squared distances are
    returned instead (this computation is faster).
  }
}
\value{
  A square matrix whose \code{[i,j]} entry is the distance
  between the points numbered \code{i} and \code{j}.
}
\details{
  This is a method for the generic function \code{pairdist}.

  Given a three-dimensional point pattern \code{X}
  (an object of class \code{"pp3"}),
  this function computes the Euclidean distances between all pairs of
  points in \code{X}, and returns the matrix of distances.

  Alternatively if \code{periodic=TRUE} and the window containing \code{X} is a
  box, then the distances will be computed in the `periodic'
  sense (also known as `torus' distance): opposite faces of the
  box are regarded as equivalent.
  This is meaningless if the window is not a box.

  If \code{squared=TRUE} then the \emph{squared} Euclidean distances
  \eqn{d^2} are returned, instead of the Euclidean distances \eqn{d}.
  The squared distances are faster to calculate, and are sufficient for
  many purposes (such as finding the nearest neighbour of a point).
}
\seealso{
  \code{\link{pairdist}},
  \code{\link{crossdist}},
  \code{\link{nndist}},
  \code{\link{K3est}}
}
\examples{
   X <- runifpoint3(20)
   d <- pairdist(X)
   d <- pairdist(X, periodic=TRUE)
   d <- pairdist(X, squared=TRUE)
}
\author{
  Adrian Baddeley
  \email{Adrian.Baddeley@csiro.au}
  \url{http://www.maths.uwa.edu.au/~adrian/}
  based on two-dimensional code by 
  Pavel Grabarnik.
}
\keyword{spatial}
\keyword{math}