I cannot duplicate your results.
T=:10000000000000306999999999997669x
9!:11 ]20
T^0.5
3162277660168427.5
<.T^0.5
3162277660168428
T1=:10000000000000306999999999997669
T1^0.5
3162277660168428
<.T1^0.5
3162277660168428
9!:14 ''
j602/2008-03-03/16:45
IFUNIX
0
IF64
0
--
David Mitchell
On 1/19/2010 3:55, R.E. Boss wrote:
> T=:10000000000000306999999999997669x
>
> 9!:11 ]20 NB. print precision
>
> T^0.5
> 3162277660168428
>
> T^0.5 appears to be integer and so<. leaves it unchanged
>
> T<....@^0.5
> 3162277660168427
>
> Special code http://www.jsoftware.com/help/dictionary/special.htm :
>
> <....@f both also>....@f ; avoids non-integer intermediate results
> on extended precision integers
>
>
> 41 43 47 53| */p:i.16
> 0 0 0 0
>
>
> R.E. Boss
>
>
> -----Oorspronkelijk bericht-----
> Van: [email protected]
> [mailto:[email protected]] Namens Gerry J
> Verzonden: dinsdag 19 januari 2010 8:22
> Aan: Programming forum
> Onderwerp: [Jprogramming] difficulty with extended precision arithmetic
>
> Hello,
>
> although i programmed APL for a few years a long time ago, i am new to J.
> I am trying to perform extended precision integer arithmetic.
>
> T, a global has been assigned this value
> 10000000000000306999999999997669x
> Then i perform this
> x=:x:<.T^0.5
> x
> 3162277660168428
>
> The correct square root from another source is
> 3162277660168427.8729609771283143493714513369669538
> so i would expect to get
> 316227766016842* 7* as the floor, not 316227766016842 *8*
>
> from the result obtained, (3162277660168428)^2 is more than T, so it
> would appear not to be the correct floor of square root of T.
>
> How should i code to get 3162277660168427 for<.T^0.5?
> (apart from subtracting 1 :-) )
>
>
> I also computed */ for all primes up to 41 then up to 53 and tried to
> get the residue of the result for each of the primes involved.
> I expected to get zeroes, but for the cases ending at 53 i was getting
> some non zero.
>
> DP=:80, is there some other configuration variable that is relevant or
> do i need to code these differently?
>
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