class FinancialCalculator::Nper
Calculates the number of periods in an annuity
Attributes
@return [Numeric] The ending value of the annuity. Defaults to 0 @api public
@return [Boolean] Whether the payment is made at the beginning of the
period (true) or end of the period (false)
@api public
@return [Numeric] The amount of each payment made @api public
@return [Numeric] The current value of the annuity @api public
@return [Numeric] The rate used for calculating the number of payments @api public
@return [DecNum] Result of the PMT calculation @api public
Public Class Methods
Create a new object for calculating the periodic payment of an ordinary annuity @param [Numeric] rate The discount (interest) rate @param [Numeric] payment The amount of each payment made @param [Numeric] present_value
The current value of the annuity @param [Numeric] future_value
The ending value of the annuity @param [Boolean] pay_at_beginning. Whether the payment is made at the beginning
of the period (true) or end of the period (false)
@return [FinancialCalculator::Nper] An instance of NPER calculation
# File lib/financial_calculator/nper.rb, line 39 def initialize(rate, payment, present_value, future_value = 0, pay_at_beginning = false) validate_numerics(rate: rate, payment: payment, present_value: present_value, future_value: future_value) @rate = Flt::DecNum(rate.to_s) @payment = Flt::DecNum(payment.to_s) @present_value = Flt::DecNum(present_value.to_s) @future_value = Flt::DecNum(future_value || "0") @pay_at_beginning = pay_at_beginning || false @result = solve(@rate, @payment, @present_value, @future_value, @pay_at_beginning) end
Public Instance Methods
# File lib/financial_calculator/nper.rb, line 56 def inspect "NPER(#{result})" end
@return [Boolean] Whether the payments are made at the beginning of each period @api public
# File lib/financial_calculator/nper.rb, line 52 def pays_at_beginning? @pay_at_beginning end
Private Instance Methods
# File lib/financial_calculator/nper.rb, line 62 def solve(rate, pmt, pv, fv, pay_at_beginning) type = pay_at_beginning ? 1 : 0 initial = pmt * (1 + rate * type) # TODO: Insert better error handling if either argument is negative. @result = Math.log((initial - fv * rate) / (initial + pv * rate)) / Math.log(1.0 + rate) end