// Calculate sensitivities
    public static void Sensitivities()
    {
        #region Inputs
        // Start input
        Date refDate = new Date(2019, 2, 25);

        // I populate market rates set: from file, from real time, ...
        RateSet mktRates = new RateSet(refDate);

        // Depos
        mktRates.Add(1.243e-2, "1m", BuildingBlockType.EURDEPO);
        mktRates.Add(1.435e-2, "3m", BuildingBlockType.EURDEPO);
        mktRates.Add(1.720e-2, "6m", BuildingBlockType.EURDEPO);
        // Swap Vs 6M
        mktRates.Add(1.869e-2, "1Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(2.316e-2, "2Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(2.544e-2, "3Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(2.745e-2, "4Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(2.915e-2, "5Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.057e-2, "6Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.175e-2, "7Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.273e-2, "8Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.362e-2, "9Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.442e-2, "10Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.589e-2, "12Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.750e-2, "15Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.835e-2, "20Y", BuildingBlockType.EURSWAP6M);
        mktRates.Add(3.787e-2, "25Y", BuildingBlockType.EURSWAP6M);

        // I shift 1bp up 10y swap input rate
        int     IndexShifted = 12;
        RateSet mktRates2    = mktRates.ShiftedRateSet(IndexShifted, 0.0001);

        // print out first and second market input rates
        for (int i = 0; i < mktRates.Count; i++)
        {
            Console.WriteLine("First: {0} {1}  Second: {2} {3}", mktRates.Item(i).M.GetPeriodStringFormat(), mktRates.Item(i).V, mktRates2.Item(i).M.GetPeriodStringFormat(), mktRates2.Item(i).V);
        }
        #endregion end Inputs

        #region building curve

        // First curve: using markets rates
        SingleCurveBuilderInterpBestFit <OnLogDf, SimpleCubicInterpolator> c1 = new SingleCurveBuilderInterpBestFit <OnLogDf, SimpleCubicInterpolator>(mktRates);
        // Second curve: like c1 but 10Y input rate is shifted
        SingleCurveBuilderInterpBestFit <OnLogDf, SimpleCubicInterpolator> c2 = new SingleCurveBuilderInterpBestFit <OnLogDf, SimpleCubicInterpolator>(mktRates2);
        string swapTenor = "10y"; // you can change it
        #endregion end building curve

        #region myFunction
        Func <SwapStyle, IRateCurve, double> NPV = (BB, c) =>
        {
            #region FixLeg
            // fixed leg data
            double[] yfFixLeg = BB.scheduleLeg1.GetYFVect(BB.swapLeg1.DayCount); // fixed is leg 1

            // dfs array of fixed lag
            Date[] dfDates = BB.scheduleLeg1.payDates; // serial date of fixed lag (each dates we should find df)

            // # of fixed cash flows
            int n_fix = dfDates.Length;

            double NPV_fix = 0.0;
            // calculate df
            for (int i = 0; i < n_fix; i++)
            {
                NPV_fix += c.Df(dfDates[i]) * yfFixLeg[i] * BB.rateValue;  // df*yf
            }
            // NPV_fix *= BB.rateValue;
            #endregion

            #region FloatLeg
            // fixed leg data
            double[] yfFloatLeg = BB.scheduleLeg2.GetYFVect(BB.swapLeg2.DayCount); // float is leg 2

            // dfs array of fixed lag
            Date[] dfDatesFloat = BB.scheduleLeg2.payDates; // serial date of float lag (each dates we should find df)

            Date[] toDateFloat = BB.scheduleLeg2.toDates;

            // # of fixed cash flows
            int n_float = dfDatesFloat.Length;

            double[] fwd = new double[n_float];

            fwd[0] = ((1 / c.Df(toDateFloat[0])) - 1) / refDate.YF(toDateFloat[0], Dc._Act_360);;
            for (int i = 1; i < n_float; i++)
            {
                double yf     = toDateFloat[i - 1].YF(toDateFloat[i], Dc._Act_360);
                double df_ini = c.Df(toDateFloat[i - 1]);
                double df_end = c.Df(toDateFloat[i]);
                fwd[i] = ((df_ini / df_end) - 1) / yf;
            }

            double NPV_float = 0.0;
            // calculate df
            for (int i = 0; i < n_float; i++)
            {
                NPV_float += c.Df(dfDatesFloat[i]) * yfFloatLeg[i] * fwd[i];  // df*yf
            }

            #endregion
            return(NPV_fix - NPV_float);
        };
        #endregion

        #region Print results

        // test forward swap starting in ref date (it should be like simple spot swap)
        double swapRate = c1.SwapFwd(refDate, swapTenor);

        // I create the swap according to standard convention
        SwapStyle y = (SwapStyle) new BuildingBlockFactory().CreateBuildingBlock(refDate, swapRate, swapTenor, BuildingBlockType.EURSWAP6M);

        // initial NPV
        double iniMTM = NPV(y, c1) * 100000000;

        // print out
        Console.WriteLine("IRS to be priced tenor: {0}. IRS to be priced rate: {1:f5}", swapTenor, swapRate);
        Console.WriteLine("{0} swap ATM fwd according the starting curve: {1:f5}. Starting P&L {2:f}", swapTenor, swapRate, iniMTM);
        Console.WriteLine("Let's shift {0} rate from {1:f5} to {2:f5}", mktRates.Item(IndexShifted).M.GetPeriodStringFormat(), mktRates.Item(IndexShifted).V, mktRates2.Item(IndexShifted).V);

        // NPV after shift
        double endMTM = NPV(y, c2) * 100000000;
        Console.WriteLine("{0} swap ATM fwd after shifting: {1:f5}. P&L after shifting {2:f}", swapTenor, c2.SwapFwd(refDate, swapTenor), endMTM);
        Console.WriteLine("Press a key to continue"); Console.ReadLine();
        #endregion
    }