# NOT RUN {
fa = letters[1:10]
circos.par(cell.padding = c(0, 0, 0, 0), track.margin = c(0, 0))
circos.initialize(fa, xlim = cbind(rep(0, 10), runif(10, 0.5, 1.5)))
circos.track(ylim = c(0, 1), track.height = mm_h(5),
    panel.fun = function(x, y) {
        circos.lines(c(0, 0 + mm_x(5)), c(0.5, 0.5), col = "blue")
    })
circos.par(track.margin = c(0, mm_h(2)))
circos.track(ylim = c(0, 1), track.height = convert_height(1, "cm"),
    panel.fun = function(x, y) {
        xcenter = get.cell.meta.data("xcenter")
        circos.lines(c(xcenter, xcenter), c(0, cm_y(1)), col = "red")
    })
circos.par(track.margin = c(0, mm_h(5)))
circos.track(ylim = c(0, 1), track.height = inch_h(1),
    panel.fun = function(x, y) {
        line_length_on_x = cm_x(1*sqrt(2)/2)
        line_length_on_y = cm_y(1*sqrt(2)/2)
        circos.lines(c(0, line_length_on_x), c(0, line_length_on_y), col = "orange")
    })
circos.clear()
# }
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