Générateur de nombres aléatoires

Bonjours, je travaille sur un programme qui a besoin de générer aléatoirement plusieurs nombres rapidement (plus d'une fois par seconde).
Avant j'utilisait ce bout de code

Code:

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#include <ctime>   int Random(int a, int b) { int nombre_aleatoire = 0; srand(time(NULL)); nombre_aleatoire = rand(); return rand()%(b-a) +a; }

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Cependant il est basé sur l'horloge interne et cela ne suffit pas pour ce projet. Comment générer de nombreux nombres par seconde?

Merci d'avance

srand se fait une fois par execution du programme, pas par nombre généré.

Encore pire alors... Comment avoir un bon générateur?

Salut,

Ce que Jean-Marc.Bourguet veut dire, c'est que tu doit appeler srand(time(NULL)); seulement au début du programme. Après, rand(); te renverra une suite de valeur pseudo-aléatoire. Si tu n'execute pas ton programme plus d'une fois par seconde, ça marchera :ccool:.

Bonjour,

si tu ne souhaites modifier que ta fonction Random, tu peux tricher en y ajoutant une variable static qui définira ou non si le rand a déjà été seedé/initialisé ou non.

Voici un petit "programme" qui génére des séries de 300 000 000 nombres pseudo aléatoire avec C++11 et Boost et son log (pour le temps) (compilé avec g++ 4.6)

Code:

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// g++ -Wall -Wextra -std=c++0x -O3 -lboost_random-mt -lboost_date_time-mt random_with_boost.cpp -o random_with_boost   #include <iostream> #include <string> #include <cstdlib> #include <ctime>   #include <boost/date_time.hpp> #include <boost/random.hpp>     int main() { // Numbers of iterations (generate) unsigned int const NB_ITERATIONS = 300*1000*1000; // Number of runs unsigned int const NB_RUNS = 10;   std::cout << "Numbers of iterations (generate) = " << NB_ITERATIONS << "\n" << std::endl;   std::cout << "std way with generator: " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution std::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 std::mt19937 engine;   // Generator auto generator = std::bind(distribution, engine);   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate a uniform integral variate between 0 and 99 generator(); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "std way using the distribution and the engine objects: " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution std::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 std::mt19937 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost mt19937 using the distribution and the engine objects: " << std::endl; std::cout << "(good uniform distribution in up to 623 dimensions) " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 boost::random::mt19937 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost mt19937_64 using the distribution and the engine objects: " << std::endl; std::cout << "(good uniform distribution in up to 311 dimensions) " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 boost::random::mt19937_64 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost mt11213b using the distribution and the engine objects: " << std::endl; std::cout << "(good uniform distribution in up to 350 dimensions) " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // mt11213b boost::random::mt11213b engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost taus88 using the distribution and the engine objects: " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // taus88 boost::random::taus88 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost hellekalek1995 using the distribution and the engine objects: " << std::endl; std::cout << "(good uniform distribution in several dimensions) " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 boost::random::hellekalek1995 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "Boost rand48 using the distribution and the engine objects: " << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Distibution boost::random::uniform_int_distribution<int> distribution(0, 99); // Mersenne twister MT19937 boost::random::rand48 engine;   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { // Generate another sample directly using the distribution and the engine objects distribution(engine); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "rand() C (not uniform)" << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Init seed srand(time(0));   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { rand(); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   std::cout << "rand() C (uniform)" << std::endl; for (unsigned int i = 0 ; i < NB_RUNS; ++i) { // Init seed srand(time(0));   // Benchmark starts boost::posix_time::ptime t0 = boost::posix_time::microsec_clock::local_time();   // Generate ! for (unsigned int j = 0; j < NB_ITERATIONS; ++j) { rand() / static_cast<int>(((unsigned int)RAND_MAX + 1) / 100); }   // Benchmark ends boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time(); boost::posix_time::time_duration time = boost::posix_time::time_period(t0, t1).length(); std::cout << "\t" << time << " => " << (static_cast<double>(time.hours()*60*60*1000*1000+time.minutes()*60*1000*1000+time.seconds()*1000*1000+time.fractional_seconds()) / NB_ITERATIONS) << " fractional seconds per number" << std::endl; } std::cout << std::endl;   return 0; }

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Code:

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$ ./random_with_boost Numbers of iterations (generate) = 300000000   std way with generator: 00:00:12.235693 => 0.0407856 fractional seconds per number 00:00:12.229781 => 0.0407659 fractional seconds per number 00:00:12.237954 => 0.0407932 fractional seconds per number 00:00:12.236913 => 0.0407897 fractional seconds per number 00:00:12.209662 => 0.0406989 fractional seconds per number 00:00:12.218766 => 0.0407292 fractional seconds per number 00:00:12.221103 => 0.040737 fractional seconds per number 00:00:12.209020 => 0.0406967 fractional seconds per number 00:00:12.227114 => 0.040757 fractional seconds per number 00:00:12.230510 => 0.0407684 fractional seconds per number   std way using the distribution and the engine objects: 00:00:12.236971 => 0.0407899 fractional seconds per number 00:00:12.240194 => 0.0408006 fractional seconds per number 00:00:12.236063 => 0.0407869 fractional seconds per number 00:00:12.257284 => 0.0408576 fractional seconds per number 00:00:12.312273 => 0.0410409 fractional seconds per number 00:00:12.238539 => 0.0407951 fractional seconds per number 00:00:12.233851 => 0.0407795 fractional seconds per number 00:00:12.231100 => 0.0407703 fractional seconds per number 00:00:12.246313 => 0.040821 fractional seconds per number 00:00:12.238724 => 0.0407957 fractional seconds per number   Boost mt19937 using the distribution and the engine objects: (good uniform distribution in up to 623 dimensions) 00:00:02.099571 => 0.00699857 fractional seconds per number 00:00:02.097383 => 0.00699128 fractional seconds per number 00:00:02.096195 => 0.00698732 fractional seconds per number 00:00:02.097780 => 0.0069926 fractional seconds per number 00:00:02.093299 => 0.00697766 fractional seconds per number 00:00:02.093257 => 0.00697752 fractional seconds per number 00:00:02.099024 => 0.00699675 fractional seconds per number 00:00:02.095079 => 0.0069836 fractional seconds per number 00:00:02.096816 => 0.00698939 fractional seconds per number 00:00:02.095166 => 0.00698389 fractional seconds per number   Boost mt19937_64 using the distribution and the engine objects: (good uniform distribution in up to 311 dimensions) 00:00:12.899464 => 0.0429982 fractional seconds per number 00:00:12.897733 => 0.0429924 fractional seconds per number 00:00:12.904572 => 0.0430152 fractional seconds per number 00:00:12.995296 => 0.0433177 fractional seconds per number 00:00:12.911522 => 0.0430384 fractional seconds per number 00:00:12.913597 => 0.0430453 fractional seconds per number 00:00:12.909714 => 0.0430324 fractional seconds per number 00:00:12.924398 => 0.0430813 fractional seconds per number 00:00:12.922247 => 0.0430742 fractional seconds per number 00:00:12.921794 => 0.0430726 fractional seconds per number   Boost mt11213b using the distribution and the engine objects: (good uniform distribution in up to 350 dimensions) 00:00:02.045992 => 0.00681997 fractional seconds per number 00:00:02.040450 => 0.0068015 fractional seconds per number 00:00:02.038793 => 0.00679598 fractional seconds per number 00:00:02.041030 => 0.00680343 fractional seconds per number 00:00:02.037519 => 0.00679173 fractional seconds per number 00:00:02.035079 => 0.0067836 fractional seconds per number 00:00:02.038874 => 0.00679625 fractional seconds per number 00:00:02.037677 => 0.00679226 fractional seconds per number 00:00:02.037807 => 0.00679269 fractional seconds per number 00:00:02.038259 => 0.0067942 fractional seconds per number   Boost taus88 using the distribution and the engine objects: 00:00:01.423849 => 0.00474616 fractional seconds per number 00:00:01.427411 => 0.00475804 fractional seconds per number 00:00:01.427113 => 0.00475704 fractional seconds per number 00:00:01.429120 => 0.00476373 fractional seconds per number 00:00:01.427980 => 0.00475993 fractional seconds per number 00:00:01.428401 => 0.00476134 fractional seconds per number 00:00:01.430246 => 0.00476749 fractional seconds per number 00:00:01.426620 => 0.0047554 fractional seconds per number 00:00:01.431298 => 0.00477099 fractional seconds per number 00:00:01.430916 => 0.00476972 fractional seconds per number   Boost hellekalek1995 using the distribution and the engine objects: (good uniform distribution in several dimensions) 00:01:09.428275 => 0.231428 fractional seconds per number 00:01:09.578160 => 0.231927 fractional seconds per number 00:01:09.408205 => 0.231361 fractional seconds per number 00:01:09.439403 => 0.231465 fractional seconds per number 00:01:09.361174 => 0.231204 fractional seconds per number 00:01:09.334417 => 0.231115 fractional seconds per number 00:01:09.359006 => 0.231197 fractional seconds per number 00:01:09.487160 => 0.231624 fractional seconds per number 00:01:09.389659 => 0.231299 fractional seconds per number 00:01:09.339894 => 0.231133 fractional seconds per number   Boost rand48 using the distribution and the engine objects: 00:00:01.692610 => 0.00564203 fractional seconds per number 00:00:01.691292 => 0.00563764 fractional seconds per number 00:00:01.693223 => 0.00564408 fractional seconds per number 00:00:01.692846 => 0.00564282 fractional seconds per number 00:00:01.692767 => 0.00564256 fractional seconds per number 00:00:01.694532 => 0.00564844 fractional seconds per number 00:00:01.691050 => 0.00563683 fractional seconds per number 00:00:01.693428 => 0.00564476 fractional seconds per number 00:00:01.689255 => 0.00563085 fractional seconds per number 00:00:01.693609 => 0.00564536 fractional seconds per number   rand() C (not uniform) 00:00:04.205507 => 0.0140184 fractional seconds per number 00:00:04.209344 => 0.0140311 fractional seconds per number 00:00:04.218483 => 0.0140616 fractional seconds per number 00:00:04.215717 => 0.0140524 fractional seconds per number 00:00:04.218569 => 0.0140619 fractional seconds per number 00:00:04.214491 => 0.0140483 fractional seconds per number 00:00:04.209880 => 0.0140329 fractional seconds per number 00:00:04.208638 => 0.0140288 fractional seconds per number 00:00:04.208381 => 0.0140279 fractional seconds per number 00:00:04.217976 => 0.0140599 fractional seconds per number   rand() C (uniform) 00:00:04.208446 => 0.0140282 fractional seconds per number 00:00:04.211523 => 0.0140384 fractional seconds per number 00:00:04.213089 => 0.0140436 fractional seconds per number 00:00:04.214194 => 0.0140473 fractional seconds per number 00:00:04.214306 => 0.0140477 fractional seconds per number 00:00:04.206771 => 0.0140226 fractional seconds per number 00:00:04.212156 => 0.0140405 fractional seconds per number 00:00:04.210910 => 0.0140364 fractional seconds per number 00:00:04.208316 => 0.0140277 fractional seconds per number 00:00:04.207850 => 0.0140262 fractional seconds per number

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Merci bien ca fonctionne! Je testerais ton générateur si j'ai besoin de plus de rapidité d'éxécution Ehonn :lol:

Ce n'est pas qu'une question de rapidité, je pense que c'est la bonne façon de faire en C++ (norme de 2011).
Tu écris une fonction qui te donne un nombre pseudo-aléatoire sur une distribution (non uniforme) entre a et b alors que ça existe déjà.