Infinity is a float.
3!:0]_
8
Extended precision arithmetic does not promote to float, so rather than
reaching infinity, it reaches a limit error. At least that is how think
about it.
Best, Cliff
On 2/17/2015 2:23 PM, Fausto Saporito wrote:
Hello,
yes the number is very big, but why if I don't use the extended
precision I have "infinity" as result, and if I use it I got an error
?
I should get infinity anyways.
this is my J session:
^/ 2 2 2 2
65536
^/ 2 2 2 2 2 NB. do not use extended precision and I have "+inf"
_
^/ 2 2 2 2 2 2 NB. do not use extended precision and I have "+inf"
_
^/ x: 2 2 2 2 2 NB. using extended precision I have the result (part of it)
2003529930406846464979072351560255750447825475569751419265016973710894059556311453089506130880933348101038234342907263181822949382118812668869506364761547029165041871916351587966347219442930927982084309104855990570159318959639524863372367203002916969592156...
^/ x: 2 2 2 2 2 2 NB. using extended precision I have error... not "+inf"
|limit error
| ^/x:2 2 2 2 2 2
https://en.wikipedia.org/wiki/Knuth%27s_up-arrow_notation
thanks,
Fausto
2015-02-17 18:55 GMT+01:00 'Pascal Jasmin' via Programming
<[email protected]>:
2 ^. ^/ 5 # 2x
65536
so at just 5, it is a 65k bit number
at 6, the 2log of that number would be that 65kbit number. The number of atoms
in the universe is an 80 bit number.
----- Original Message -----
From: Raul Miller <[email protected]>
To: Programming forum <[email protected]>
Cc:
Sent: Tuesday, February 17, 2015 12:32 PM
Subject: Re: [Jprogramming] Fwd: Hello all!
I would guess that the number you are generating is too big to be
represented using J's data structures (which would also suggest that
it would be too big to fit into memory).
Thanks,
--
Raul
On Tue, Feb 17, 2015 at 12:12 PM, Fausto Saporito
<[email protected]> wrote:
HI!
I'm a new J user with a little experience of APL and LISP.
In these days I'm playing with big numbers... very big indeed, and I
found a bug (?) in the exteded precision implementation of J.
I'm not sure if I can call it a bug, but if I use the standard
precision number I got a "infinity" as result... as should be.
I'm talking about knuth-up-arrow notation, to build the "tower of
power". In J the syntax is amazingly simple : ^/ 2 2 2 2
2^^4 is 2 * (2* (2* 2)) = 65536
Now 2^^5 is _ with standard precision... but if I use x: (i.e. ^/ x:
2 2 2 2 2) can get most of number... it's quite big indeed.
The problem arises with 2^^6 or 3^^4 I get "limit error" instead of _ ... why ?
Is it an expected behaviour ?
thanks in advance,
Fausto
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