public const double tol = 0.001;
public delegate double fx(double x);
public static fx composeFunctions(fx f1, fx f2) {
return (double x) => f1(x) + f2(x);
public static fx f_xirr(double p, double dt, double dt0) {
return (double x) => p*Math.Pow((1.0+x),((dt0-dt)/365.0));
public static fx df_xirr(double p, double dt, double dt0) {
return (double x) => (1.0/365.0)*(dt0-dt)*p*Math.Pow((x+1.0),(((dt0-dt)/365.0)-1.0));
public static fx total_f_xirr(double[] payments, double[] days) {
fx resf = (double x) => 0.0;
for (int i = 0; i < payments.Length; i++) {
resf = composeFunctions(resf,f_xirr(payments[i],days[i],days[0]));
public static fx total_df_xirr(double[] payments, double[] days) {
fx resf = (double x) => 0.0;
for (int i = 0; i < payments.Length; i++) {
resf = composeFunctions(resf,df_xirr(payments[i],days[i],days[0]));
public static double Newtons_method(double guess, fx f, fx df) {
public static void Main (string[] args)
double[] payments = {-6800,1000,2000,4000};
double[] days = {01,08,16,25};
double xirr = Newtons_method(0.1,
total_f_xirr(payments,days),
total_df_xirr(payments,days));
Console.WriteLine("XIRR value is {0}", xirr);