x.max <- 10
y.max <- 10
y1 <- 2
y2 <- 7.8
vector.y <- c(y1, y2)
vector.x  <- c(2, 5, 8)
vector.xx <- c(0.5, 3.5, 6.5, 9.5)
al <- (y2 - y1) * 0.3
m.y <- mean(vector.y)
xy.rand <- data.frame(
	"x" = runif(1000, 0, x.max),
	"y" = runif(1000, m.y - 0.7, m.y + 0.7)
)

# -----------------------------------------------------------------------------------
set.frame <- function()
{
	par(mar = c(0, 0, 0, 0))
	plot(
		numeric(0), numeric(0),
		xlim = c(0, x.max),
		ylim = c(0, x.max),
		axes = FALSE,
		xlab = "",
		ylab = ""
	)
}
set.line <- function(vector.x, vector.y, margin.width = 1.3)
{
	x <- range(vector.x) + c(-margin.width, margin.width)
	for (y in vector.y) {
		lines(c(0, x.max), c(y, y), lty = 3, lwd = 2)
		lines(x, c(y, y), lty = 1, lwd = 2)
	}
}
set.points <- function(y, pch, bg)
{
	points(
		vector.x,
		rep(y, length(vector.x)),
		cex = 8,
		pch = pch,
		col = "#000000",
		bg = bg
	)
}
set.arrows <- function(vector.x, y.start, y.end)
{
	for (x in vector.x) {
		arrows(
			x, y.start, x, y.end,
			lwd = 2,
			col = "#666666"
		)
	}
}
set.cloud <- function(xy.rand)
{
	points(
		xy.rand$x,
		xy.rand$y,
		pch = "/",
		col = "#999999"
	)
}
set.status <- function(vector.x, y, key)
{
	sapply(
		1:length(vector.x),
		function(i) {
			text(
				vector.x[i],
				y,
				eval(parse(text =
					sprintf("expression(%s[%i])", key, i)
				)),
				cex = 2,
				adj = c(0.4, 0.5)
			)
			
		}
	)
}

plot.schema <- function()
{
	set.frame()
	set.line(vector.x, vector.y)
	set.points(y1, 21, "#ff8000")
	set.points(y2, 22, "#ffff00")
	set.arrows(vector.x, m.y + al, m.y - al)
	set.cloud(xy.rand)

	text(0, y1 - 1.6, "Observable world (data)", pos = 4, cex = 1.5)
	text(0, y2 + 1.8, "Real world (population)", pos = 4, cex = 1.5)
	set.status(vector.x, y2, "x")
	set.status(vector.x, y1, "y")
}

plot.interactons <- function(vector.x, y, w1, w2, col = "#0000ff")
{
	for (x in vector.x) {
		arrows(x - w1, y, x - w2, y, lwd = 3, col = col)
		arrows(x + w1, y, x + w2, y, lwd = 3, col = col)
		points(x, y, pch = "?", cex = 1.5, col = col)
	}
}

# -----------------------------------------------------------------------------------
plot.schema()
plot.interactons(vector.xx, y2 + 0.6, 0.2, 0.8)