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Ruby RNG that returns a normal distribution between two integers
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| # MIT License | |
| # Copyright (c) 2020 Ross Becker | |
| # | |
| # Permission is hereby granted, free of charge, to any person obtaining a copy | |
| # of this software and associated documentation files (the "Software"), to deal | |
| # in the Software without restriction, including without limitation the rights | |
| # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | |
| # copies of the Software, and to permit persons to whom the Software is | |
| # furnished to do so, subject to the following conditions: | |
| # | |
| # The above copyright notice and this permission notice shall be included in all | |
| # copies or substantial portions of the Software. | |
| # | |
| # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
| # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
| # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
| # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
| # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | |
| # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | |
| # SOFTWARE. | |
| class GaussianRandom | |
| attr_reader :min, :max, :mean, :deviation, :results | |
| def initialize(min, max, deviation: 3.5) | |
| @min, @max = min, max | |
| @mean = min + ((max - min) / 2.0) | |
| @deviation = (max - min) / 2.0 / deviation | |
| @results = [] | |
| end | |
| def call | |
| r = nil | |
| until (min..max).cover? r | |
| results.push(*box_muller(mean, deviation)) if results.empty? | |
| r = results.shift | |
| end | |
| return r | |
| end | |
| private | |
| def box_muller(mean, deviation) | |
| s = nil | |
| until (0.0..1.0).cover? s | |
| v1 = 2.0 * Kernel.rand - 1.0; | |
| v2 = 2.0 * Kernel.rand - 1.0; | |
| s = v1 * v1 + v2 * v2; | |
| end | |
| s = Math.sqrt((-2.0 * Math.log(s)) / s); | |
| return (mean+(v1*s)*deviation).round, (mean+(v2*s)*deviation).round | |
| end | |
| end | |
| # USE: | |
| # rng = GaussianRandom.new( MIN_VAL, MAX_VAL), rng.call | |
| # You can change the distribution by passing an optional distribution parameter, lower numbers will spread the curve. | |
| # | |
| rn_gauss = GaussianRandom.new(3,8) | |
| dist = Array.new(10000) { rn_gauss.call }.each_with_object(Hash.new(0)) { |val,h| h[val] += 1 }.sort | |
| puts "Dist: #{dist}" | |
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