amortization.rb in finrb-0.1.1

- old
+ new

@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
-require_relative "cashflows"
-require_relative "decimal"
-require_relative "transaction"
+require_relative 'cashflows'
+require_relative 'decimal'
+require_relative 'transaction'
 
 module Finrb
   # the Amortization class provides an interface for working with loan amortizations.
   # @note There are _two_ ways to create an amortization.  The first
   #   example uses the amortize method for the Numeric class.  The second
@@ -32,10 +32,30 @@
     attr_reader :principal
     # @return [Array] the interest rates used for calculating the amortization
     # @api public
     attr_reader :rates
 
+    # @return [DecNum] the periodic payment due on a loan
+    # @param [DecNum] principal the initial amount of the loan or investment
+    # @param [Rate] rate the applicable interest rate (per period)
+    # @param [Integer] periods the number of periods needed for repayment
+    # @note in most cases, you will probably want to use rate.monthly when calling this function outside of an Amortization instance.
+    # @example
+    #   rate = Rate.new(0.0375, :apr, :duration => (30 * 12))
+    #   rate.duration #=> 360
+    #   Amortization.payment(200000, rate.monthly, rate.duration) #=> DecNum('-926.23')
+    # @see https://en.wikipedia.org/wiki/Amortization_calculator
+    # @api public
+    def self.payment(principal, rate, periods)
+      if rate.zero?
+        # simplified formula to avoid division-by-zero when interest rate is zero
+        -(principal / periods).round(2)
+      else
+        -(principal * (rate + (rate / (((rate + 1)**periods) - 1)))).round(2)
+      end
+    end
+
     # create a new Amortization instance
     # @return [Amortization]
     # @param [DecNum] principal the initial amount of the loan or investment
     # @param [Rate] rates the applicable interest rates
     # @param [Proc] block
@@ -52,11 +72,11 @@
       compute
     end
 
     # compare two Amortization instances
     # @return [Numeric] -1, 0, or +1
-    # @param [Amortization]
+    # @param [Amortization] other
     # @api public
     def ==(other)
       (principal == other.principal) && (rates == other.rates) && (payments == other.payments)
     end
 
@@ -154,29 +174,9 @@
     #   amt = 300000.amortize(rate)
     #   amt.interest[0,6].sum #=> DecNum('5603.74')
     # @api public
     def interest
       @transactions.filter_map { |trans| trans.amount if trans.interest? }
-    end
-
-    # @return [DecNum] the periodic payment due on a loan
-    # @param [DecNum] principal the initial amount of the loan or investment
-    # @param [Rate] rate the applicable interest rate (per period)
-    # @param [Integer] periods the number of periods needed for repayment
-    # @note in most cases, you will probably want to use rate.monthly when calling this function outside of an Amortization instance.
-    # @example
-    #   rate = Rate.new(0.0375, :apr, :duration => (30 * 12))
-    #   rate.duration #=> 360
-    #   Amortization.payment(200000, rate.monthly, rate.duration) #=> DecNum('-926.23')
-    # @see https://en.wikipedia.org/wiki/Amortization_calculator
-    # @api public
-    def self.payment(principal, rate, periods)
-      if rate.zero?
-        # simplified formula to avoid division-by-zero when interest rate is zero
-        -(principal / periods).round(2)
-      else
-        -(principal * (rate + (rate / (((1 + rate)**periods) - 1)))).round(2)
-      end
     end
 
     # @return [Array] the amount of the payment in each period
     # @example find the total payments for a loan
     #   rate = Rate.new(0.0375, :apr, :duration => (30 * 12))