Random numbers: Difference between revisions

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The goal of this task is to generate a 1000-element array (vector, list, whatever it's called in your language) filled with normally distributed random numbers with a mean of 1.0 and a [http://en.wikipedia.org/wiki/Standard_deviation standard deviation] of 0.5
The goal of this task is to generate a 1000-element array (vector, list, whatever it's called in your language) filled with normally distributed random numbers with a mean of 1.0 and a [http://en.wikipedia.org/wiki/Standard_deviation standard deviation] of 0.5

Many libraries only generate uniformly distributed random numbers. If so, use [http://en.wikipedia.org/wiki/Normal_distribution#Generating_values_for_normal_random_variables this formula] to convert them to a normal distribution.


{{header|Ada}}
{{header|Ada}}
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{{header|E}}
{{header|E}}

accum [] for _ in 1..1000 { _.with(entropy.nextGaussian()) }
accum [] for _ in 1..1000 { _.with(entropy.nextGaussian()) }


{{header|IDL}}
{{header|IDL}}

result = 1.0 + 0.5*randomn(seed,1000)
result = 1.0 + 0.5*randomn(seed,1000)


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{{header|Pop11}}
{{header|Pop11}}

;;; Choose radians as arguments to trigonometic functions
;;; Choose radians as arguments to trigonometic functions
true -> popradians;
true -> popradians;
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{{header|Tcl}}
{{header|Tcl}}

proc nrand {} {return [expr sqrt(-2*log(rand()))*cos(4*acos(0)*rand())]}
proc nrand {} {return [expr sqrt(-2*log(rand()))*cos(4*acos(0)*rand())]}
for {set i 0} {$i < 1000} {incr i} {lappend result [expr 1+.5*nrand()]}
for {set i 0} {$i < 1000} {incr i} {lappend result [expr 1+.5*nrand()]}

Revision as of 21:47, 17 September 2007

Task
Random numbers
You are encouraged to solve this task according to the task description, using any language you may know.

The goal of this task is to generate a 1000-element array (vector, list, whatever it's called in your language) filled with normally distributed random numbers with a mean of 1.0 and a standard deviation of 0.5

Many libraries only generate uniformly distributed random numbers. If so, use this formula to convert them to a normal distribution.

Ada

with Ada.Numerics.Float_Random; use Ada.Numerics.Float_Random;
with Ada.Numerics.Generic_Elementary_Functions;

procedure Normal_Random is
   Seed : Generator;
   function Normal_Distribution(Seed : Generator) return Float is
      package Elementary_Flt is new 
         Ada.Numerics.Generic_Elementary_Functions(Float);
      use Elementary_Flt;
      use Ada.Numerics;
      R1 : Float;
      R2 : Float;
      Mu : constant Float := 1.0;
      Sigma : constant Float := 0.5;
   begin
      R1 := Random(Seed);
      R2 := Random(Seed);
      return Mu + (Sigma * Sqrt(-2.0 * Log(X => R1, Base => 10.0)) * 
         Cos(2.0 * Pi * R2));
   end Normal_Distribution;
      
   type Normal_Array is array(1..1000) of Float;
   Distribution : Normal_Array;
begin
   Reset(Seed);
   for I in Distribution'range loop
      Distribution(I) := Normal_Distribution(Seed);
   end loop;
end Normal_Random;

C plus plus

#include <cstdlib>   // for rand
#include <cmath>     // for atan, sqrt, log, cos
#include <algorithm> // for generate_n

double const pi = 4*std::atan(1.0);

// simple functor for normal distribution
class normal_distribution
{
public:
  normal_distribution(double m, double s): mu(m), sigma(s) {}
  double operator() // returns a single normally distributed number
  {
    double r1 = (std::rand() + 1.0)/(RAND_MAX + 1.0); // gives equal distribution in (0, 1]
    double r2 = (std::rand() + 1.0)/(RAND_MAX + 1.0);
    return mu + sigma * std::sqrt(-2*std::log(r1))*std::cos(2*pi*r2);
  }
private:
  double mu, sigma;
};

int main()
{
  double array[1000];
  std::generate_n(array, 1000, normal_distribution(1.0, 0.5));
}

E

accum [] for _ in 1..1000 { _.with(entropy.nextGaussian()) }

IDL

result = 1.0 + 0.5*randomn(seed,1000)

Java

double[] list = new double[1000];
Random rng = new Random();
for(int i = 0;i<list.length;i++) {
  list[i] = 1.0 + 0.5 * rng.nextGaussian()
}

MAXScript

randList = #()
for i in 1 to 1000 do append randList (random 0.0 2.0)

Perl

map {.5 + rand} 1..1000

Pop11

;;; Choose radians as arguments to trigonometic functions
true -> popradians;
;;; procedure generating standard normal distribution
define random_normal() -> result;
lvars r1 = random0(1.0), r2 = random0(1.0);
     cos(2*pi*r1)*sqrt(-2*log(r2)) -> result
enddefine;
lvars array, i;
;;; Put numbers on the stack
for i from 1 to 1000 do 1.0+0.5*random_normal() endfor;
;;; collect them into array
consvector(1000) -> array;

Python Interpreter: Python 2.5

import random
randList = [random.gauss(1, .5) for i in range(1000)]

Tcl

proc nrand {} {return [expr sqrt(-2*log(rand()))*cos(4*acos(0)*rand())]}
for {set i 0} {$i < 1000} {incr i} {lappend result [expr 1+.5*nrand()]}