EFL Simulation.js

var baseline_coc = 0.06; // What baseline investment should we compare this program to?
var annual_interest = 0.08; // What interest rate will we charge residents if they abandon their initiative?
var initial_loan = 50000.0; // Assume everyone begins with a $50K debt
var minimum_payment = { 'active': 500, 'inactive': 1000 } // If someone's initiative is active, offer a reduced minimum payment ($500/m) compared to $1000/m otherwise

var annual_deactivation_probability = 0.3; // How likely is it in any given year than an initiative shuts down?

var yearly_enrollment = [5, 10, 15, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20]; // Over the first 15 years, how many residents are enrolled per year?

// Variables of interest we'll be measuring over the course of runs
var total_paid = 0;
var lost_interest = 0;
var profit_over_baseline = 0;
var t = 0;

var Member = function() {
    var self = this;
    self.t_born = t;
    self.t_dead = null;
    self.age_at_death = null;
    self.active = true;
    self.balance = initial_loan; 
    self.minimum_annual_payment = self.active ? minimum_payment['active'] : minimum_payment['inactive'];

    self.pay = function(amount) { // For a given Member, pay back `amount` of their loan
        total_paid += amount;
        self.balance -= amount;
    };

    self.grow_balance = function() { // Increment the balance each year
        if (self.active) {
            self.balance += 0;
            lost_interest += annual_interest * self.balance;
        } else {
            self.balance *= (1 + annual_interest);
            profit_over_baseline += (annual_interest - baseline_coc) * self.balance;
        }
    };

    self.increment_year = function() { // Increment the year
        if (self.active) {
            if (Math.random() < annual_deactivation_probability) { // Simulate deactivation and record timeline if deactivating
                self.active = false;
                self.t_dead = t;
                self.age_at_death = self.t_dead - self.t_born;
            }
        }
        self.pay(self.minimum_annual_payment);
        self.grow_balance();
    };

    self.get_age = function () {
    	return t - self.t_born;
    }
};

var run = function() { // Simulate a run
	t = 0;
    total_paid = 0;
    lost_interest = 0;
    profit_over_baseline = 0;


    var members = [];

    // For each of the 15y of the program, simulate members' growth over time
    yearly_enrollment.forEach(function(count) {
        for (var i = 0; i < count; ++i) {
            members.push(new Member());
        };

        members.forEach(function(member) {
            member.increment_year();
        });
        t += 1;
    });

    // Log results
    var results = {};
    results["Total alumni"] = members.length;
    var active_alumni = members.filter(function(m) {
        return m.active;
    });
    results["Total active alumni"] = active_alumni.length;
    var inactive_alumni = members.filter(function(m) { return !m.active; });
    results["age_at_death"] = inactive_alumni.map(function(m) { return m.age_at_death; }).reduce(function(a,b) { return a + b; })/inactive_alumni.length;
    results["Average living age"] = active_alumni.map(function(m) { return m.get_age(); }).reduce(function(a,b) { return a + b; })/active_alumni.length;
    results["Invested principal"] = 50000 * members.length;
    results["Outstanding balances"] = members.map(function(m) {
        return m.balance;
    }).reduce(function(a, b) {
        return a + b;
    });
    results["Total paid"] = total_paid;
    results["Lost interest"] = lost_interest;
    results["Profit from inactive members"] = profit_over_baseline;
    results["Net cost"] = profit_over_baseline - lost_interest;

    return results;
};


// Simulate over num_runs (10K) runs
var num_runs = 10000;
var runs = [];
for (var i = 0; i < num_runs; ++i) {
    runs.push(run());
};

// Average simulation results
var average = {};
Object.keys(runs[0]).forEach(function(key) {
    average[key] = runs.map(function(r) {
        return r[key];
    }).reduce(function(a, b) {
        return a + b;
    }) / runs.length;
});

// Log out results
console.log(average);

///////////////////////////////////////////////////////////////////////////////
// Sample run results (10K)
//
// { 'Total alumni': 270,
//   'Total active alumni': 46.1633,
//   age_at_death: 1.6657111417978643,
//   'Average living age': 3.213380739663558,
//   'Invested principal': 13500000,
//   'Outstanding balances': 20044032.82097633,
//   'Total paid': 985000,
//   'Lost interest': 2030810.98,
//   'Profit from inactive members': 2032838.8616636116,
//   'Net cost': 2027.8816636019956 }