Code tweak and tidy, fixed rhubarb spawning

statistics.lua

@@ -1,9 +1,9 @@
 local statistics = {}
-
 local ROOT_2 = math.sqrt(2.0)
 
 -- Approximations for erf(x) and erfInv(x) from
---    https://en.wikipedia.org/wiki/Error_function
+-- https://en.wikipedia.org/wiki/Error_function
+
 local erf
 local erf_inv
 
@@ -13,19 +13,26 @@ local C = 2.0/(math.pi * A)
 local D = 1.0 / A
 
 erf = function(x)
+
 	if x == 0 then return 0; end
+
 	local xSq  = x * x
 	local aXSq = A * xSq
 	local v = math.sqrt(1.0 - math.exp(-xSq * (B + aXSq) / (1.0 + aXSq)))
+
 	return (x > 0 and v) or -v
 end
 
 erf_inv = function(x)
+
 	if x == 0 then return 0; end
+
 	if x <= -1 or x >= 1 then return nil; end
+
 	local y = math.log(1 - x * x)
 	local u = C + 0.5 * y
 	local v = math.sqrt(math.sqrt(u * u - D * y) - u)
+
 	return (x > 0 and v) or -v
 end
 
@@ -37,6 +44,7 @@ local poisson
 local cdf_table = {}
 
 local function generate_cdf(lambda_index, lambda)
+
 	local max = math.ceil(4 * lambda)
 	local pdf = math.exp(-lambda)
 	local cdf = pdf
@@ -56,6 +64,7 @@ for li = 1, 100 do
 end
 
 poisson = function(lambda, max)
+
 	if max < 2 then
 		return (math.random() < math.exp(-lambda) and 0) or 1
 	elseif lambda >= 2 * max then
@@ -67,6 +76,7 @@ poisson = function(lambda, max)
 	local cdfs = cdf_table[lambda_index]
 
 	if cdfs then
+
 		lambda = 0.25 * lambda_index
 
 		if u < cdfs[0] then return 0; end
@@ -74,9 +84,13 @@ poisson = function(lambda, max)
 		if u >= cdfs[max - 1] then return max; end
 
 		if max > 4 then  -- Binary search
+
 			local s = 0
+
 			while s + 1 < max do
+
 				local m = math.floor(0.5 * (s + max))
+
 				if u < cdfs[m] then max = m; else s = m; end
 			end
 		else
@@ -88,6 +102,7 @@ poisson = function(lambda, max)
 		return max
 	else
 		local x = lambda + math.sqrt(lambda) * std_normal(u)
+
 		return (x < 0.5 and 0) or (x >= max - 0.5 and max) or math.floor(x + 0.5)
 	end
 end
@@ -102,14 +117,17 @@ statistics.erf_inv = erf_inv
  --
  -- @return
  --    Any real number (actually between -3.0 and 3.0).
- --
+
 statistics.std_normal = function()
+
 	local u = math.random()
+
 	if u < 0.001 then
 		return -3.0
 	elseif u > 0.999 then
 		return 3.0
 	end
+
 	return std_normal(u)
 end
 
@@ -121,14 +139,17 @@ end
  --    The distribution standard deviation.
  -- @return
  --    Any real number (actually between -3*sigma and 3*sigma).
- --
+
 statistics.normal = function(mu, sigma)
+
 	local u = math.random()
+
 	if u < 0.001 then
 		return mu - 3.0 * sigma
 	elseif u > 0.999 then
 		return mu + 3.0 * sigma
 	end
+
 	return mu + sigma * std_normal(u)
 end
 
@@ -140,11 +161,14 @@ end
  --    The distribution maximum.
  -- @return
  --    An integer between 0 and max (both inclusive).
- --
+
 statistics.poisson = function(lambda, max)
+
 	lambda, max = tonumber(lambda), tonumber(max)
+
 	if not lambda or not max or lambda <= 0 or max < 1 then return 0; end
+
 	return poisson(lambda, max)
 end
 
-return statistics
+return statistics