Unbias a random generator: Difference between revisions

=={{header|Lua}}==

<lang lua>

local function randN(n)

if n < 3 or n > 6 then error "Invalid bias" end

local chance = 1/n

return function()

if math.random() < chance then return 1 else return 0 end

end

end

local function unbiased(n)

local biased = randN (n)

return function()

local a, b = biased(), biased()

while a==b do

a, b = biased(), biased()

end

return a

end

end

local function demonstrate (samples)

for n = 3, 6 do

biased = randN(n)

unbias = unbiased(n)

local bcounts = {[0]=0,[1]=0}

local ucounts = {[0]=0,[1]=0}

for i=1, samples do

local bnum = biased()

local unum = unbias()

bcounts[bnum] = bcounts[bnum]+1

ucounts[unum] = ucounts[unum]+1

end

print(string.format("N = %d",n),

"# 0", "# 1",

"% 0", "% 1")

print("biased", bcounts[0], bcounts[1],

bcounts[0] / samples * 100,

bcounts[1] / samples * 100)

print("unbias", ucounts[0], ucounts[1],

ucounts[0] / samples * 100,

ucounts[1] / samples * 100)

end

end

demonstrate(100000)

</lang>

Output:

<pre>

N = 3 # 0 # 1 % 0 % 1

biased 66832 33168 66.832 33.168

unbias 50207 49793 50.207 49.793

N = 4 # 0 # 1 % 0 % 1

biased 75098 24902 75.098 24.902

unbias 49872 50128 49.872 50.128

N = 5 # 0 # 1 % 0 % 1

biased 80142 19858 80.142 19.858

unbias 50049 49951 50.049 49.951

N = 6 # 0 # 1 % 0 % 1

biased 83407 16593 83.407 16.593

unbias 49820 50180 49.82 50.18

</pre>