Excel RATE function in .NET CORE

Question

I tried to use RATE function in .NET CORE project. There is a Visual Basic library I wanted to use but it does not work with .NET CORE. https://docs.microsoft.com/en-us/dotnet/api/microsoft.visualbasic.financial.rate?view=netframework-4.7.2

Are there any other ways to use it or should I calculate it explicitly? How? I can't find any explanation of this function.

Answer 1

According to @omajid comment I transform official VB code to C#. This is all you need to use Rate method without dependency on Microsoft.VisualBasic.dll which is lacking this method in .NET CORE.

private double Rate(double NPer, double Pmt, double PV, double FV = 0, DueDate Due = DueDate.EndOfPeriod, double Guess = 0.1)
{
    double dTemp;
    double dRate0;
    double dRate1;
    double dY0;
    double dY1;
    int I;

    // Check for error condition
    if (NPer <= 0.0)
        throw new ArgumentException("NPer must by greater than zero");

    dRate0 = Guess;
    dY0 = LEvalRate(dRate0, NPer, Pmt, PV, FV, Due);
    if (dY0 > 0)
        dRate1 = (dRate0 / 2);
    else
        dRate1 = (dRate0 * 2);

    dY1 = LEvalRate(dRate1, NPer, Pmt, PV, FV, Due);

    for (I = 0; I <= 39; I++)
    {
        if (dY1 == dY0)
        {
            if (dRate1 > dRate0)
                dRate0 = dRate0 - cnL_IT_STEP;
            else
                dRate0 = dRate0 - cnL_IT_STEP * (-1);
            dY0 = LEvalRate(dRate0, NPer, Pmt, PV, FV, Due);
            if (dY1 == dY0)
                throw new ArgumentException("Divide by zero");
        }

        dRate0 = dRate1 - (dRate1 - dRate0) * dY1 / (dY1 - dY0);

        // Secant method of generating next approximation
        dY0 = LEvalRate(dRate0, NPer, Pmt, PV, FV, Due);
        if (Math.Abs(dY0) < cnL_IT_EPSILON)
            return dRate0;

        dTemp = dY0;
        dY0 = dY1;
        dY1 = dTemp;
        dTemp = dRate0;
        dRate0 = dRate1;
        dRate1 = dTemp;
    }

    throw new ArgumentException("Can not calculate rate");
}

private double LEvalRate(double Rate, double NPer, double Pmt, double PV, double dFv, DueDate Due)
{
    double dTemp1;
    double dTemp2;
    double dTemp3;

    if (Rate == 0.0)
        return (PV + Pmt * NPer + dFv);
    else
    {
        dTemp3 = Rate + 1.0;
        // WARSI Using the exponent operator for pow(..) in C code of LEvalRate. Still got
        // to make sure that they (pow and ^) are same for all conditions
        dTemp1 = Math.Pow(dTemp3, NPer);

        if (Due != 0)
            dTemp2 = 1 + Rate;
        else
            dTemp2 = 1.0;
        return (PV * dTemp1 + Pmt * dTemp2 * (dTemp1 - 1) / Rate + dFv);
    }
}

private const double cnL_IT_STEP = 0.00001;
private const double cnL_IT_EPSILON = 0.0000001;

enum DueDate
{
    EndOfPeriod = 0,
    BegOfPeriod = 1
}