[Edu-sig] re: financial calculation

[Arthur]

For anybody who might join me in my crass interest in $4.5 billion.

In the form below - i.e. just adding some sanity checking  - I seem to be
able to conclude my code is sane (by some loose definition of sanity). 

Sample  output:

value at 2004-12-27: 64.50
assumed value at 2005-02-11: 65.50
projected future value at 2014-12-15: 218.64

value at 2004-12-27: 64.50
assumed value at 2005-02-11: 71.00
projected future value at 2014-12-15: 131297.27

value at 2004-12-27: 64.50
actual at 2005-02-11: 81.00
projected future value at 2014-12-15: 4561078546.84

------------------------------------------------------------------
from __future__ import division

import datetime
import math

def future_value(iday,cday,ivalue,cvalue,years):
    days_invested=(cday-iday).days
    year_periods=365/days_invested
    annualized_rate = math.log(cvalue/ivalue)*year_periods
    #future_value at the end of given years
    return ivalue*math.pow(math.e,annualized_rate*years)

#date we purchased stock
iday=datetime.date(2004,12,27)

#date of valuation
cday=datetime.date(2005,2,11)

#10 years from date we purchased stock
fdate =  iday+datetime.timedelta(weeks=10*52)

#price at purchase
ivalue=64.5

for i in range(0,34):
   cvalue = ivalue + i/2
   fvalue = round(future_value(iday,cday,ivalue,cvalue,10),2)
   print "value at %s: %.2f" %(iday,ivalue)
   if not i == 33:
      print "assumed value at %s: %.2f" %(cday,cvalue)
   else:
      print "actual value at %s: %.2f" %(cday,cvalue)
   print "projected future value at %s: %.2f" %(fdate,fvalue)
   print "+-------------------------------+"
   print "\n"