exponential.cc

// g++ -lfmt exponential.cc -o exponential && ./exponential <lambda>
//
// Using lambda 0.3
//  01:  1% 00189 - ***
//  02:  2% 00275 - *****
//  03:  3% 00330 - ******
//  04:  4% 00430 - ********
//  05:  6% 00613 - ************
//  06:  8% 00839 - ****************
//  07: 11% 01104 - **********************
//  08: 14% 01467 - *****************************
//  09: 20% 02038 - ****************************************
//  10: 27% 02715 - ******************************************************
// useful samples 70%
//
#include <cstdio>
#include <random>
#include <fmt/core.h>
#include <fmt/ranges.h>

size_t samples = 10000;

size_t min =  1;
size_t max = 10;

float lambda = 0.3;   // default lambda

int main(int argc, char *argv[]) {
    if (argc == 2) {
        lambda = atof(argv[1]);
    }
    fmt::print("Using lambda {}\n", lambda);
    std::vector<size_t> b(10);
    std::default_random_engine re{std::random_device{}()};
    std::exponential_distribution<> dist(lambda);

    size_t n = 0;
    for(int s = 0; s < samples; ++n) {
        auto val = int(dist(re));
        if (val >= min && val <= max) {   // val in [1;10]
            ++b[max - val];
            ++s;
        }
    }
    for(size_t i = 0; i < b.size(); i++) {
        fmt::print(" {:02}: {:2}% {:05} - {}\n",
                i + 1, b[i]*100/samples, b[i], std::string(b[i]/50, '*'));
    }
    fmt::print("useful samples {:02}%\n", samples * 100/n);
    return 0;
}