public static decimal MonthlyPayment(decimal rate, int periods, decimal presentValue, decimal futureValue, PaymentType type)
{
if (rate == 0)
{
return((presentValue - futureValue) / periods);
}
decimal t = (int)type;
return(((presentValue * DecimalMath.Pow(1 + rate, periods)) - futureValue) / ((1 + (rate * t)) * ((DecimalMath.Pow(1 + rate, periods) - 1) / rate)));
}
public static decimal PresentValue(decimal rate, int periods, int elapsedPeriods, decimal monthlyPayment, decimal futureValue, PaymentType type)
{
if (rate == 0)
{
return(futureValue + (monthlyPayment * (periods - elapsedPeriods)));
}
if (elapsedPeriods == periods)
{
return(futureValue);
}
decimal t = (int)type;
return(((monthlyPayment * (1 + (rate * t)) * ((DecimalMath.Pow(1 + rate, periods - elapsedPeriods) - 1) / rate)) + futureValue) / DecimalMath.Pow(1 + rate, periods - elapsedPeriods));
}
public static decimal Rate(int periods, decimal presentValue, decimal futureValue, decimal monthlyPayment, PaymentType type)
{
decimal t = (int)type;
decimal N0 = periods;
decimal guess = ((monthlyPayment * periods) - presentValue) / presentValue;
try
{
return(NewtonRaphson.Iterate(
(decimal r0) => (((presentValue * DecimalMath.Pow(1M + r0, periods)) - futureValue) / ((1M + (r0 * t)) * ((DecimalMath.Pow(1M + r0, periods) - 1) / r0))) - monthlyPayment,
(decimal r0) => ((futureValue * ((N0 * r0 * r0 * t * DecimalMath.Pow(1M + r0, periods)) + (periods * r0 * DecimalMath.Pow(1M + r0, periods)) - (r0 * DecimalMath.Pow(1M + r0, periods)) - DecimalMath.Pow(1M + r0, periods) + r0 + 1)) + (presentValue * DecimalMath.Pow(1M + r0, periods) * ((-N0 * r0 * r0 * t) + DecimalMath.Pow(1M + r0, periods) + (r0 * (DecimalMath.Pow(1 + r0, periods) - periods - 1)) - 1))) / ((r0 + 1) * (DecimalMath.Pow(1 + r0, periods) - 1) * (DecimalMath.Pow(1 + r0, periods) - 1) * ((r0 * t) + 1) * ((r0 * t) + 1)),
guess));
}
catch (IterationsExceededException <decimal> exc)
{
return(exc.LastValue);
}
}
public static decimal FutureValue(int periods, decimal presentValue, decimal rate, decimal monthlyPayment, PaymentType type)
{
decimal t = (int)type;
return(Math.Round(-1 * (((1 + (rate * t)) * ((DecimalMath.Pow(1 + rate, periods) - 1) / rate) * monthlyPayment) - (presentValue * DecimalMath.Pow(1 + rate, periods))), 8));
}