#' @param Sigma symmetric, positive-definite square matrix of order 2. The dispersion matrix.
#' @param beta positive real number. The shape of the distribution.
#' @param xlim,ylim x-and y- limits.
#' @param n A one or two element vector giving the number of steps in the x and y grid, passed to \code{\link{plot3d.function}}.
#' @param n A one or two element vector giving the number of steps in the x and y grid, passed to \code{\link[rgl]{plot3d.function}}.
#' @param xvals,yvals The values at which to evaluate \code{x} and \code{y}. If used, \code{xlim} and/or \code{ylim} are ignored.
#' @param xlab,ylab,zlab The axis labels.
#' @param col The color to use for the plot. See \code{\link{plot3d.function}}.
#' @param col The color to use for the plot. See \code{\link[rgl]{plot3d.function}}.
#' @param tol tolerance (relative to largest variance) for numerical lack of positive-definiteness in Sigma, for the estimation of the density. see \code{\link{dmggd}}.
#' @param ... Additional arguments to pass to \code{\link{plot3d.function}}.
#' @param ... Additional arguments to pass to \code{\link[rgl]{plot3d.function}}.
#' @return Returns invisibly the probability density function.
\item{n}{A one or two element vector giving the number of steps in the x and y grid, passed to \code{\link{plot3d.function}}.}
\item{n}{A one or two element vector giving the number of steps in the x and y grid, passed to \code{\link[rgl]{plot3d.function}}.}
\item{xvals, yvals}{The values at which to evaluate \code{x} and \code{y}. If used, \code{xlim} and/or \code{ylim} are ignored.}
\item{xlab, ylab, zlab}{The axis labels.}
\item{col}{The color to use for the plot. See \code{\link{plot3d.function}}.}
\item{col}{The color to use for the plot. See \code{\link[rgl]{plot3d.function}}.}
\item{tol}{tolerance (relative to largest variance) for numerical lack of positive-definiteness in Sigma, for the estimation of the density. see \code{\link{dmggd}}.}
\item{...}{Additional arguments to pass to \code{\link{plot3d.function}}.}
\item{...}{Additional arguments to pass to \code{\link[rgl]{plot3d.function}}.}
}
\value{
Returns invisibly the probability density function.