Re: a numeric bug.
Re: a numeric bug.
- Subject: Re: a numeric bug.
- From: deivy petrescu <email@hidden>
- Date: Thu, 15 Sep 2005 17:55:47 -0400
On Sep 15, 2005, at 13:38, Christopher Nebel wrote:
On Sep 15, 2005, at 3:13 AM, Emmanuel wrote:
At 9:05 AM +0100 9/15/05, has wrote:
deivy petrescu wrote:
I don't get it. 10^23 is way below AS numeric limit (which I
believe is over 10^300).
The precision limit is much lower, however - approx. ±9e15.
Beyond that they're only approximations, and calculations
involving the least significant digits are going to have
inaccuracies.
I think that Deivy's point is that when it comes to take the "mod"
a smart computer storing 1.000 as the mantissa and 24 as the
exponent of 10 should be able to give the correct result.
Sure, but that's not how the internal representation of numbers in
AppleScript works. It's using IEEE 754 double-precision numbers,
which use mantissa * 2**exponent, which is notoriously inaccurate
when representing powers of 10. (10 is an infinite repeating
decimal in base 2.)
--Chris Nebel
AppleScript and Automator Engineering
First, I am a bit less stressed now than when I found the errors :)
Second, I see, now, yesterday I did not, that to use (mod ) AS needs
to keep the whole number to give an accurate answer.
However, I would assume that, and most people would probably agree,
that rounding or precision errors (except for propagation) should
happen in a far, far away decimal place. I would even accept
pi= 3.15
or
pi=3.0
But,
pi=10
would blow me away.
Somehow I feel that if a program offers the tool and makes no point
on the limits of the tool, something is really wrong. This goes for
AppleScript, and as has pointed out, for Python as well.
If you want arbitrary precision or strict financial math, you're
using the wrong language, and you should stop one or the other.
Chris, I am well aware that you know Smile.
Many people may not know it and know that is a full fledge Scientific
software used in many scientific institutions.
Someone in one of these institutions might one day need to use
something like 10^23 mod 29.
Boy, is he in for a surprise!
I have no problem with AS shortcomings, if you will, but I'd
appreciate some documentation.
As many people, or one person over and over again, I can't
remember... :), pointed out the great benefit of AppleScript is
having it being used in a way that it was not originally thought for.
Please document it. At least now I can find 10^24 mod 29 in AS or
Smile, because I am aware of the problem. Thus, I can stil use Smile,
or AS, and avoid the traps.
Thanks
deivy
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