# To box in an area under a four-parameter Beta quantile distribution with
# location parameters l = .25 and u = 75, and shape parameters alpha = 5 and
# beta = 3, from .4 to .6:
plot(NULL, xlim = c(0, 1), ylim = c(0, 1))
coords <- Beta.gfx.poly.qdf(from = 0.4, to = 0.6, by = 0.001, alpha = 5,
beta = 3, l = 0.25, u = 0.75)
polygon(coords)
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