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Programming-Idioms

  • Rust
  • C++

Idiom #14 Pick uniformly a random floating point number in [a..b)

Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.

#include <random>
float pick(float a, float b)
{
	std::default_random_engine generator;
	std::uniform_real_distribution distribution(a, b);
	return distribution(generator);
}

You probably want to pass a random engine into the function instead of creating a new one each time in generator.

This example doesn't seed the generator, so will generate the same result in every call.
extern crate rand;
use rand::{Rng, thread_rng};
thread_rng().gen_range(a..b);

If you need to generate a lot of random stuff, save the thread_rng as a variable so it is only initialized once.
#include <stdlib.h>
double pick(double a, double b)
{
	return a + (double)rand() / ((double)RAND_MAX * (b - a));
}

this is not uniformly distributed!!
New implementation...
< > ⌨
programming-idioms.org 
float pick(float a, float b)
{
	std::default_random_engine generator;
	std::uniform_real_distribution distribution(a, b);
	return distribution(generator);
}
thread_rng().gen_range(a..b);
double pick(double a, double b)
{
	return a + (double)rand() / ((double)RAND_MAX * (b - a));
}
  (defn rand-between [a b]
    (+ a (* (- b a) (rand))))
Random rng = new();
double pick(double a, double b)
{
    return rng.NextDouble() * (b - a) + a;
}
real pick(real _a, real _b){
    return uniform(_a, _b);
}
double pick(num a, num b) => a + new Random().nextDouble() * (b - a);
defmodule MyRandomPicker do
  def pick(a, b), do: a + (b - a) * :rand.uniform()
end
a + :rand.uniform() * (b-a)
A + (B - A) * rand:uniform().
call random_number(c)
d = a + (b-a) * c
func pick(a, b  float64)  float64 {
	return a + (rand.Float64() * (b-a))
}
pick(a,b)=
  return.(+a).(*(b-a))=<<System.Random.randomIO::IO(Double)

pick a b = do
  r <- System.Random.randomIO :: IO Double
  return a + (r * (b - a))

a + (b-a) * Math.random();
a + Math.random() * (b - a)
Random r = new Random();
double v = (r.nextDouble() * (b - a)) + a;
double pick(double a, double b){
	return a + (Math.random() * (b-a));
}
Random r = new Random();
double v = r.nextDouble(a, b);
Random.nextDouble(a,b)
(+ a (random (float (- b a))))
function pick(a,b)
	return a + (math.random()*(b-a))
end

float pick(float a,float b) {
  id<GKRandom>  rnd=GKMersenneTwisterRandomSource.sharedRandom;
  float ru;
  while ((ru=rnd.nextUniform)==1);
  return a+ru*(b-a);
}
function pick(float $a, float $b): float
{
    $rand = mt_rand() / mt_getrandmax();
    $rand *= ($b - $a);
    $rand += ($a);

    return $rand;
}
function pick(a, b:real): real;
begin
  result := a + random * (b - a);
end;

my ($min, $max) = (1.5, 7.2);
my $x = $min + rand($max-$min);
random.uniform(a,b)
rand(a...b)
def randomDraw(min: Double, max: Double): Double = {
  val range = max - min
  (random.doubleValue * range) + min
}
(+ a (* (- b a) (random 1.0)))



| rand |
rand := Random new.
rand next * (b - a) + a

Function pick(a As Double, b As Double) As Double
    Static rng As New Random()
    Return rng.NextDouble() * (b - a) + a
End Function