library(nnet)

plot.nn <- function(
	nn,
	xmin.max = c(-1, 1),
	ymin.max = c(-1, 1),
	dx = xmin.max[2] - xmin.max[1],
	dy = ymin.max[2] - ymin.max[1],
	y.padding = dy * 0.05,
	lwd.w = function(w) w * 3,
	col.w = function(w) ifelse(w > 0, "#ff400040", "#0000ff40"),
	w.min = 0.01,
	pch.i = c(22, 21, 21),
	col.i = c("#000000", "#000000", "#000000"),
	bg.i = c("#ffffff", "#ffffff", "#ffffff"),
	cex.i = function(n) { cex <- 10 / sqrt(n); min(cex, 5) },
	cex.text = 0.7
) {
	v.n <- nn$n
	list.x <- lapply(
		v.n, function(n)
		seq(xmin.max[1], xmin.max[2], length = n + 2)[2:(n + 1)]
	)
	v.y <- seq(ymin.max[1] + y.padding, ymin.max[2] - y.padding, length = 3)
	wts <- coef(nn)
	wts.normalized <- wts / sd(wts[grep("^[^b]", names(wts))])
	get.tag <- function(i, ii, ij) ifelse(
		i == 1,
		sprintf("i%i->h%i", ii, ij),
		ifelse(
			v.n[3] > 1,
			sprintf("h%i->o%i", ii, ij),
			sprintf("h%i->o", ii)
		)
	)
	get.tag.b <- function(i, ii) ifelse(
		i == 2,
		sprintf("b->h%i", ii),
		ifelse(
			v.n[3] > 1,
			sprintf("b->o%i", ii),
			sprintf("b->o", ii)
		)
	)
	# plot
	par(mar = c(0, 0, 0, 0), mgp = c(0, 0, 0))
	plot(
		numeric(0), numeric(0),
		type = "n",
		xlim = xmin.max,
		ylim = ymin.max,
		xlab = "",
		ylab = "",
		axes = FALSE
	)
	# lines
	for (i in 1:2) {
		j <- i + 1
		v.xi <- list.x[[i]]
		v.xj <- list.x[[j]]
		for (ii in 1:v.n[i]) {
			for (ij in 1:v.n[j]) {
				tag <- get.tag(i, ii, ij)
				w <- wts.normalized[tag]
				#cat(tag, "\n")
				if (abs(w) > w.min) lines(
					x = c(v.xi[ii], v.xj[ij]),
					y = c(v.y[i], v.y[j]),
					lwd = lwd.w(w),
					col = col.w(w)
				)
			}
		}
	}
	# points
	for (i in 1:3) points(
		x = list.x[[i]],
		y = rep(v.y[i], v.n[i]),
		pch = pch.i[i],
		bg = bg.i[i],
		cex = cex.i(v.n[i])
	)
	# input layer
	text(
		x = list.x[[1]],
		y = v.y[1],
		labels = nn$coefnames,
		cex = cex.text
	)
	# hidden and output layers
	for (i in 2:3) {
		v.xi <- list.x[[i]]
		for (ii in 1:v.n[i]) {
			tag <- get.tag.b(i, ii)
			text(
				v.xi[ii], v.y[i],
				sprintf("%.2f", wts[tag]),
				cex = cex.text
			)
		}
	}
}