### Name: ellipsoidhull
### Title: Compute the Ellipsoid Hull or Spanning Ellipsoid of a Point Set
### Aliases: ellipsoidhull print.ellipsoid
### Keywords: dplot hplot

### ** Examples

x <- rnorm(100)
xy <- unname(cbind(x, rnorm(100) + 2*x + 10))
exy <- ellipsoidhull(xy)
exy # >> calling print.ellipsoid()

plot(xy)
lines(predict(exy))
points(rbind(exy$loc), col = "red", cex = 3, pch = 13)

exy <- ellipsoidhull(xy, tol = 1e-7, ret.wt = TRUE, ret.sq = TRUE)
str(exy) # had small `tol', hence many iterations
(ii <- which(zapsmall(exy $ wt) > 1e-6)) # only about 4 to 6 points
round(exy$wt[ii],3); sum(exy$wt[ii]) # sum to 1