exponential_dist.cpp

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#include <cassert>    // For assert
#include <cmath>      // For std::pow
#include <iostream>   // For I/O operation
#include <stdexcept>  // For std::invalid_argument
#include <string>     // For std::string

namespace probability {
namespace geometric_dist {
double exponential_expected(double lambda) {
    if (lambda <= 0) {
        throw std::invalid_argument("lambda must be greater than 0");
    }
    return 1 / lambda;
}

double exponential_var(double lambda) {
    if (lambda <= 0) {
        throw std::invalid_argument("lambda must be greater than 0");
    }
    return 1 / pow(lambda, 2);
}

double exponential_std(double lambda) {
    if (lambda <= 0) {
        throw std::invalid_argument("lambda must be greater than 0");
    }
    return 1 / lambda;
}
}  // namespace geometric_dist
}  // namespace probability

static void test() {
    double lambda_1 = 1;
    double expected_1 = 1;
    double var_1 = 1;
    double std_1 = 1;
 
    double lambda_2 = 2;
    double expected_2 = 0.5;
    double var_2 = 0.25;
    double std_2 = 0.5;
 
    double lambda_3 = 3;
    double expected_3 = 0.333333;
    double var_3 = 0.111111;
    double std_3 = 0.333333;
 
    double lambda_4 = 0;     // Test 0
    double lambda_5 = -2.3;  // Test negative value
 
    const float threshold = 1e-3f;
 
    std::cout << "Test for lambda = 1 \n";
    assert(
        std::abs(expected_1 - probability::geometric_dist::exponential_expected(
                                  lambda_1)) < threshold);
    assert(std::abs(var_1 - probability::geometric_dist::exponential_var(
                                lambda_1)) < threshold);
    assert(std::abs(std_1 - probability::geometric_dist::exponential_std(
                                lambda_1)) < threshold);
    std::cout << "ALL TEST PASSED\n\n";
 
    std::cout << "Test for lambda = 2 \n";
    assert(
        std::abs(expected_2 - probability::geometric_dist::exponential_expected(
                                  lambda_2)) < threshold);
    assert(std::abs(var_2 - probability::geometric_dist::exponential_var(
                                lambda_2)) < threshold);
    assert(std::abs(std_2 - probability::geometric_dist::exponential_std(
                                lambda_2)) < threshold);
    std::cout << "ALL TEST PASSED\n\n";
 
    std::cout << "Test for lambda = 3 \n";
    assert(
        std::abs(expected_3 - probability::geometric_dist::exponential_expected(
                                  lambda_3)) < threshold);
    assert(std::abs(var_3 - probability::geometric_dist::exponential_var(
                                lambda_3)) < threshold);
    assert(std::abs(std_3 - probability::geometric_dist::exponential_std(
                                lambda_3)) < threshold);
    std::cout << "ALL TEST PASSED\n\n";
 
    std::cout << "Test for lambda = 0 \n";
    try {
        probability::geometric_dist::exponential_expected(lambda_4);
        probability::geometric_dist::exponential_var(lambda_4);
        probability::geometric_dist::exponential_std(lambda_4);
    } catch (std::invalid_argument& err) {
        assert(std::string(err.what()) == "lambda must be greater than 0");
    }
    std::cout << "ALL TEST PASSED\n\n";
 
    std::cout << "Test for lambda = -2.3 \n";
    try {
        probability::geometric_dist::exponential_expected(lambda_5);
        probability::geometric_dist::exponential_var(lambda_5);
        probability::geometric_dist::exponential_std(lambda_5);
    } catch (std::invalid_argument& err) {
        assert(std::string(err.what()) == "lambda must be greater than 0");
    }
    std::cout << "ALL TEST PASSED\n\n";
}

int main() {
    test();  // Self test implementation
    return 0;
}