factorial of negative one (-1)
Bj Raz
whitequill.bj at gmail.com
Mon Nov 1 13:52:44 CET 2010
On Nov 1, 2010, at 5:42 AM, Hrvoje Niksic <hniksic at xemacs.org> wrote:
> Chris Rebert <clp2 at rebertia.com> writes:
>
>> (2) The underlying double-precision floating-point number only has ~16
>> decimal digits of precision, so it's pointless to print out "further"
>> digits.
>
> A digression which has nothing to do with Raj's desire for "better
> accuracy"...
>
> Printing out further digits (without quotes) is not pointless if you
> want to find out the exact representation of your number in python's
> floating point, for educational purposes or otherwise. Python has a
> little-known but very instructive method for determining the makeup of a
> float:
>
>>>> 1.1 .as_integer_ratio()
> (2476979795053773, 2251799813685248)
>
> 1.1 is represented with the closest fraction with a power-of-two
> denominator, 2476979795053773/2251799813685248. As is the case with all
> Python floats, this fraction has an exact decimal representation,
> 1.100000000000000088817841970012523233890533447265625. It is not that
> unreasonable to request that the whole number be printed, and python
> will happily oblige:
>
>>>> "%.100g" % 1.1
> '1.100000000000000088817841970012523233890533447265625'
>
> The digits after the first cluster of zeros are not garbage, at least
> not in the sense of what you get reading uninitialized memory and such;
> they're mathematically precise decimal digits of the number that "1.1"
> has turned into during conversion to float.
Thank you Chris.
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