#!/usr/bin/python """A finance library for Python. All interest rates are to be expressed in decimal notation (i.e. 0.0825 instead of 8.25) This library has been placed in the public domain. Version history: 1.0 - 2001-01 - Initial program - Rupert Scammell <rupe@yak.net> 2.0 - 2001-03 - Additions and revisions by Louis Luangkesorn <lluang@northwestern.edu> (compound interest present value, equivalent value of an annuity) 2.1 - 2004-01 - Readability changes by Matthew Scott <spud@goldenspud.com> """ import sys import math def simpleInterest(p, r, t): """Simple interest Returns: interest value Input values: See 'Simple interest future value' below """ i = p * r * t return i def simpleInterestFutureValue(p, r, t): """Simple interest future value Returns: future value Input values: p : principal r : Interest rate (decimal) t : Investment periods """ fv = p * (1 + r * t) return fv def compoundedInterest(fv, p): """Compounded interest Returns: Interest value Input values: fv : Future value p : Principal """ i = fv - p return i def compoundInterestFutureValue(p, r, c, n): """Compound interest future value Returns: future value Input values: p : principal r : interest rate c : number of compounding periods in a year n : (c * t) , total number of compounding periods """ fv = (p * (1 + (r / c))) ** n return fv def annualYield(r, c): """Annual yield Returns: Simple interest rate necessary to yield the same amount of dollars yielded by the annual rate r compounded c times for one year Input values: r : interest rate c : number of compounding periods in a year """ y = ((1 + (r / c)) ** c) - 1 return y def ordinaryAnnuity(pymt, p, r, c, n): """Ordinary annuity formula Returns: future value Input values: pymt : payment made during compounding period p : principal r : annual interest rate c : number of compounding periods in a year n : total number of payments """ block1 = ((1 + (r / c)) ** n) - 1 block2 = r / c fv = pymt * (block1 / block2) return fv def presentValueAnnuity(pymt, r, c, n): """Present value of an annuity Returns: Lump sum that can be deposited at the beginning of the annuity's term, at the same interest rate and with the same compounding period, that would yield the same amount as the annuity. Input values: See 'Ordinary annuity formula' above.""" ipp = r / c pval = pymt * ((1 - ((1 + ipp) ** (-n))) / ipp) return pval def equivalentAnnualCost(pval, r, c, n): """Equivalent value of an annuity Returns: Coupon amount for an annuity given the present value Input values: pval : present value of annuity r : annual interest rate c : number of compounding periods in a year n : total number of payments See 'Ordinary annuity formula' above. """ ipp = r / c pymt = pval / ((1 - ((1 + ipp) ** (-n))) / ipp) return pymt def amortization(loan, r, c, n): """Amortization Returns: The amount of money that needs to be paid at the end of each period to get rid of the total loan. Input values: loan : Total loan amount r : annual interest rate c : number of compounding periods a year n : total number of compounding periods """ ipp = r / c amt = (loan * ipp) / (1 - ((1 + ipp) ** (-n))) return amt def compoundInterestPresentValue(p, r, c, n): """Compound interest present value Returns: present value Input values: p : principal r : interest rate c : number of compounding periods in a year n : (c * t), total number of compounding periods """ pv = (p / ((1 + (r / c)) ** n)) return pv

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