hypertree = function(ans, hres = 50., xsh = 0.04, drop = (max(h) - min(h))/12., 
	labspace = drop/1.9 + padx, padx = 0.05, cex = 0.8, xline, lab,
	titlecex = 1.15)
{
	# This algorithm was originally written with
	#    y as merge height
	#    x as groups id
	# and then transposed
	# The notation is not consistent 
	x = match(1.:length(ans$order), ans$order)
	h = ans$height
	join = ans$merge
	join.n = nrow(join)
	ngrp.x = rep(NA, join.n)
	ngrp.y = h
	if(missing(lab))
		lab = as.character(1.:(join.n + 1.))
	rx = c(min(h) - drop - labspace, max(h) + padx)
	ry = c(0.5, length(x) + 0.5)
	panelScale(rx = rx, ry = ry)
	if(missing(xline)) {
		xline = panelInbounds(rx)
		xline = xline[xline > min(h)]
	}
	axis(side=1,at=xline,tck=1,labels=F, col = "#AFAFAF")
      axis(side=1,at=xline,tck=0,mgp = c(1,.1,0),cex.axis=cex)
      mtext(side=1,line=1.2,"Merge Height",cex=cex)
	mtext(side=3, line=.5, "Cluster Tree", cex=titlecex)
    
	grp1 = join[, 1]
	grp2 = join[, 2]
	for(i in 1.:join.n) {
		g1 = grp1[i]
		g2 = grp2[i]
		if(g1 < 0.) {
			g1 = abs(g1)
			grp1.x = x[g1]
			grp1.y = h[i] - drop
			text(grp1.y - xsh, grp1.x, lab[g1], adj = 1., cex
				 = cex, col = 1.)
		}
		else {
			grp1.x = ngrp.x[g1]
			grp1.y = ngrp.y[g1]
		}
		if(g2 < 0.) {
			g2 = abs(g2)
			grp2.x = x[g2]
			grp2.y = h[i] - drop
			text(grp2.y - xsh, grp2.x, lab[g2], adj = 1., cex
				 = cex, col = 1.)
		}
		else {
			grp2.x = ngrp.x[g2]
			grp2.y = ngrp.y[g2]
		}
		ym = h[i]
		k1 = (grp1.y/ym - 2.)^2.
		k2 = (grp2.y/ym - 2.)^2.
		c1 = ifelse(k1 > 1.,  - sqrt(k1 - 1.),  - sqrt(1. - k1))
		c2 = ifelse(k2 > 1., sqrt(k2 - 1.), sqrt(1. - k2))
		xm = (c1 * grp2.x - c2 * grp1.x)/(c1 - c2)
		# save the new peak 
		#ngrp.x[i] = (grp1.x+grp2.x)/2
		b = (grp2.x - xm)/c2
		# plot the hyperbola
		ngrp.x[i] = xm
		px = seq(grp1.x, grp2.x, length = hres)
		py =  - ym * sqrt(1. + ((px - xm)/b)^2.) + 2. * ym
		#segments(ngrp.y[i],grp1.x,ngrp.y[i],grp2.x)
		#segments(grp1.x,ngrp.y[i],grp1.x,grp1.y)
		#segments(grp2.x,ngrp.y[i],grp2.x,grp2.y)
		# plot the lines 
		lines(py, px, col = "#FF0000", lwd = 2)
	}
	panelOutline(col = "#000000")
}