Re: Is There a Way to Rationalize a Decimal in Pari/GP?

[Rick Regan <exploringbinary@gmail.com>]

I didn't mention that I am only looking at this from a limited point
of view. I want to convert dyadic decimal fractions -- those that
represent double-precision floating-point binary values. They are
always terminating decimals.  My aim is to reduce them to the form
a/2^n, which bestappr() does (except that the power of two is given as
a constant, and not as 2^n. I can find n with factor() but if you know
of a more direct way...).

On Fri, Jun 5, 2009 at 9:40 AM, John Cremona <john.cremona@gmail.com> wrote:
> It was not supposed to be off list ;)
>
> bestappr() uses continued fractions, and cannot do better than the
> precision you give it, so it is not very clear what the "exact
> fraction" is (unless you specify the decimal expansion in such detail
> that the full period is seen!)
>
> John
>
> 2009/6/5 Rick Regan <exploringbinary@gmail.com>:
>> Thanks Bill (and John who contacted me off list). -- bestappr() does the trick!
>>
>> In my case I always want the exact fraction, so I have to make sure I
>> specify a large enough denominator. I am converting long decimals, and
>> I don't want to count decimal places. The easy solution seems to be to
>> pass bestappr() an arbitrarily large power of 10, like
>> bestappr(0.1000000000000000055511151231257827021181583404541015626,10^100).
>>
>> Rick
>>
>> --
>> “There are 10 types of people ... those who understand binary and
>> those who don't” -- http://www.exploringbinary.com
>>
>



-- 
“There are 10 types of people ... those who understand binary and
those who don't” -- http://www.exploringbinary.com