test-econ-model/include/econ.hpp

#include <iostream>
#include <vector>
#include <random>
#include <cmath>

std::random_device econ_dev;
std::mt19937 econ_rng(econ_dev());

// ----------------------------------------------------------
// -- Recipient Finders
// ----------------------------------------------------------

/**
 * @brief Find & return random participant
 * 
 * @param balances Balance vec
 * @return int 
 */
int find_participant_random(std::vector<int> &balances) {
    // random spend ratio is too costly
    std::uniform_int_distribution<std::mt19937::result_type> dist_len(0,balances.size()-1); 
    return dist_len(econ_rng); 
}

/**
 * @brief Find & return random participant
 * 
 * @param balances Balance vec
 * @param percent_cutoff Upper N% to decide among
 * @return int 
 */
int find_participant_random_wealthy(std::vector<int> &balances, float percent_cutoff = 10) {
    // random spend ratio is too costly
    int cutoff = percent_cutoff / 100 * balances.size();
    std::uniform_int_distribution<std::mt19937::result_type> dist_len(0,balances.size()-1); 
    return dist_len(econ_rng); 
}

// ----------------------------------------------------------
// -- Spend Decisions
// ----------------------------------------------------------

/**
 * @brief Simple random economic spend decision
 * 
 * @param balances Balances vec
 * @param id ID of participant making the decision
 * @param spend_ratio Proportion of savings they are willing 
 * to spend
 */
void economic_decision_simple(std::vector<int> &balances, int id, float spend_ratio) {
    // assert(spend_ratio > 0 && spend_ratio <= 1);
    int total_bal = balances.at(id);


    int spendable = spend_ratio * total_bal;
    int recipient_id = find_participant_random(balances);
    balances.at(id) -= spendable;
    balances.at(recipient_id) += spendable;
}

/**
 * @brief Sin-based varying spend output based on age. Peaks in midlife
 *
 * @param ages Ages vec
 * @param balances Balances vec
 * @param id ID of participant making decision
 * @param max_spend_ratio max/peak spend ratio
 * @param bump how much to bump min spend amount from 0
 */
void economic_random_age_sin(
    std::vector<int> &ages,
    std::vector<int> &balances,
    int max_age,
    int id,
    float max_spend_ratio,
    int bump = 0.1
) {
    int recipient_id = find_participant_random(balances);
    int spendable = round(
        max_spend_ratio * 
        sin(ages[id] / max_age) + 
        bump)
    ;
    balances.at(id) -= spendable;
    balances.at(recipient_id) += spendable;
}