On Tue, Nov 24, 2009 at 6:47 AM, Shashwat Anand <anand.shash...@gmail.com> wrote: > Followed by this discussion on Hacker News I checked this link and was > wondering how to calculate value of 'e' to a large extent > > as e = 1/0! + 1/1! +1/2! .... and so on... > so i wrote this: >>>> sum(1.0 / math.factorial(i) for i in range(100)) > 2.7182818284590455 > > It was not giving the precision that I wanted so I tried decimal module of > which I was not much aware of. > >>>> decimal.getcontext().prec = 100 >>>> sum(decimal.Decimal(str(1./math.factorial(decimal.Decimal(i)))) for i in >>>> range(100))
You are using floating point division here. The argument to math.factorial() is an integer, so the conversion of i to Decimal is not doing anything - it is converted back to an integer. Then you compute 1./<some large integer>. This will use floating point math and will fail when the factorial is too large to represent in floating point. You should convert the result of factorial() to Decimal and compute Decimal(1.0)/Decimal(<factorial>). This should give you additional precision as well. Kent _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
