RATE()
 Computes the interest rate for a loan
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 Syntax

     RATE(<nCapital>,<nPayment>,<nNumberPayments>)
        --> nInterestRate

 Arguments

     <nCapital>  Designates the amount of the loan.

     <nPayment>  Designates the payment per installment.

     <NumberPayments>  Designates the number of the planned payment
     periods.

 Returns

     RATE() returns the loan interest rate.

 Description

     RATE() determines the annual interest rate for a loan <nCapital> in the
     <nNumberPayments> period at the specified <nPayment> installment.  The
     calculated interest rate is based on a Newtonian iterative solution
     procedure:

         lk+1=ik - f(ik)/f(ik)

     where:

         f(i)=(1-(l + i)^-n)/i - PV/PMT

     The initial value for i is selected as follows:

         -io = PMT/PV - PV/n^2PMT

 Note

     .  This function allows a maximum value for the payment period of
        1020.

 Example

     For a $2500 loan, you pay $86.67 per month for 3 years.  What is the
     effective annual interest rate?

     nLoan     :=  2500
     nPayment  :=  86.67
     nPeriod   :=  36

     ? RATE(nLoan, nPayment, nPeriod) * 12      // 0.1501 (15.01%)