Internal Rate of Return

IRR.rs

fn main() {
    let initial_investment = -1000.0;
    let cash_receipts = vec![250.0, 350.0, 450.0, 550.0];

    let cash_flows = vec![initial_investment, 
        cash_receipts[0], cash_receipts[1], cash_receipts[2], cash_receipts[3]];
        
    let rate = irr(&cash_flows);
    println!("IRR: {:.2}%", rate * 100.0);
}

fn irr(cash_flows: &[f64]) -> f64 {
    let tolerance = 0.00001;
    let mut min_rate = -0.9999;
    let mut max_rate = 1.0;
    let mut guess = 0.0;

    while max_rate - min_rate > tolerance {
        let mut sum_pv = 0.0;
        for (i, cash_flow) in cash_flows.iter().enumerate() {
            let t = i as f64;
            let pv = cash_flow / ((1.0_f64 + guess).powf(t + 1.0_f64));
            sum_pv += pv;
        }

        if sum_pv > 0.0 {
            min_rate = guess;
        } else {
            max_rate = guess;
        }
        guess = (max_rate + min_rate) / 2.0;
    }

    guess
}