wrong.
first, gcd is a general concept, it’s nothing crafted but found
it was always there and not meant for anything in the first place
it applies to rational numbers just as fine and to any scaling
thereof. Mathematically, you get sane results working with gcd
on √2*ℚ, for example.
second, the only if part is badly wrong, too.
+./ (, -) a
will work no matter a’s representation and not give an epsilon
(unless a an epsilon :-) to start with)
Am 16.05.20 um 08:26 schrieb Raul Miller:
GCD is meant for exact numbers.
It works fine with fractions, IF (and only if) the numbers you are
working with exactly represent the numbers you intend to manipulate.
For binary floating point numbers this would be sums of powers of 2
which do not exceed the precision of the representation (for current J
on 64 bit machines: all divisors have to be powers of 2, you have 53
bits of mantissa to work with and a limited range of exponents).
5r2 +. 7r2
1r2
2.5 +. 3.5
0.5
Thanks,
--
Raul
On Fri, May 15, 2020 at 11:17 PM bill lam <bbill....@gmail.com> wrote:
Yes I agree GCD meant for whole numbers, so that +. on floating points can
first convert to rational first and convert back to float afterwards
+./&.x: 4.57 4.34 4.44
0.01
x: is clever enough to find the shortest form of rational equal to the
original floating number range
(3!:3) 4.5700000000000003
e300000000000000
0800000000000000
0100000000000000
0000000000000000
48e17a14ae471240
(3!:3) 4.57
e300000000000000
0800000000000000
0100000000000000
0000000000000000
48e17a14ae471240
x: 4.5700000000000003
457r100
x: 4.57
457r100
That said, I don't see any real benefit for change, if a user want rational
number behavior, he/she can use the form
+./&.x:
On Sat, May 16, 2020 at 7:18 AM Devon McCormick <devon...@gmail.com> wrote:
Since, AFAIK, GCD was originally defined in the context of whole numbers,
you probably get what you deserve using it with non-integers.
On Fri, May 15, 2020 at 7:04 PM Raul Miller <rauldmil...@gmail.com> wrote:
It is odd, though, that even with comparison tolerance set to zero, +.
is not associative on fractional floating point values:
9!:19]0
0j16":,.+./4.57 4.34 4.44
0.0000000000000036
0j16":,.+./|.4.57 4.34 4.44
0.0000000000290870
It is commutative though:
(-:|:)+./@>{;~4.57 4.34 4.44
1
0j16":+./@>{;~4.57 4.34 4.44
4.5700000000000003 0.0100000000000655 0.0099999999999758
0.0100000000000655 4.3399999999999999 0.0200000000000466
0.0099999999999758 0.0200000000000466 4.4400000000000004
I'm not quite sure what's going on here... maybe a built in epsilon
which is independent of comparison tolerance?
Thanks,
--
Raul
On Fri, May 15, 2020 at 6:53 PM Hauke Rehr <hauke.r...@uni-jena.de>
wrote:
In case you are willing to accept labelling it a problem.
As I mentioned by altering the thread’s subject, yes,
this ain’t a bug. But there may be an opportunity for
improvement without sacrifice. Or so do I think.
Am 16.05.20 um 00:49 schrieb 'Michael Day' via Programming:
Not a new "bug" - I've still got J503 for some reason - so:
+./4.57 4.34 4.44
5.39568e_12
ABOUTJ_jijs_ NB. nearest thing to JVERSION???
Copyright 1994-2004 Jsoftware Inc.
For information about this and related products:
Jsoftware Inc.
P.O. Box 330
Excelsior, MN 55331
tel: 952 470-7345 fax: 952 470-9202
www.jsoftware.com
i...@jsoftware.com
As Devon and Henry suggest, it's the usual problem with "exact"
representation of reals.
Mike
On 15/05/2020 15:17, 'Bo Jacoby' via Programming wrote:
+./4.57 4.34 4.44
5.39568e_12
NB. this was not the correct answer. A bug?
+./x:4.57 4.34 4.44
1r100
NB. this was a work-around
Thanks!
Bo.
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Quantitative Consultant
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