Lua: How do I calculate a random number between 50 and 500, with an average result of 100?-CodePudding

I think this is a log-normal distribution? I'm not sure. The lua I have is here:

local min = 50
local max = 500
local avg = 100
local fFloat = ( RandomInt( 0, avg ) / 100 ) ^ 2 -- float between 0 and 1, squared
local iRange = max - min -- range of min-max
local fDistribution = ( ( fFloat * iRange )   min ) / 100
finalRandPerc = fDistribution * RandomInt( min, max ) / 100

It is close to working, but sometimes generates numbers that are slightly too large.

CodePudding user response：

This can be done in literally infinite number of ways. One other approach is to generate a number from binomial distribution, multiply with 450 and add 50. I will leave the task of finding the right parameters for the binomial distribution to you.

CodePudding user response：

How do I calculate a random number between 50 and 500, with an average result of 100?

You can use Chi-squared of degree 4 with its tail removed.
It is very easy to calculate.

local function random_50_500()
   -- result is from 50 to 500
   -- mean is very near to 100
   local x
   repeat
      x = math.log(math.random())   math.log(math.random())
   until x > -18
   return x * -25   50
end