circos.initialize(c("a", "b", "c", "d"), xlim = c(0, 10))
circos.track(ylim = c(0, 10), panel.fun = function(x, y) {
circos.triangle(c(2, 2), c(2, 8),
c(8, 8), c(2, 8),
c(5, 5), c(8, 2))
}, track.height = 0.5)
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