From: Marnen Laibow-Koser <marnen@...>
Date: 2009-10-29T04:30:21+09:00
Subject: Re: Ruby can't subtract ?

Robert Klemme wrote:
> On 28.10.2009 19:21, Matthew K. Williams wrote:
>>> I bash my head against the wall? :)
>> 
>> Pamphlet -> http://en.wikipedia.org/wiki/IEEE_754-2008
>> 
>> Popcorn, well, it's kinda hard to transmit over the wire. ;-)
> 
> Easy to do with a modern email client - just needs support for POP3 and
> a working firewall (for the heat). :-)

LOL!

> 
>> As a rule of thumb, if you really care about the decimals, either use 
>> BigDecimal or integers (and keep track of where the decimal should be -- 
>> this is common for $$$$).  Unfortunately, this is not limited to ruby, 
>> either -- C, Java, and a host of other languages all are subject.
> 
> Absolutely: this is a common issue in *all* programming languages which
> are not systems for symbolic math (like Mathematica) because they do not
> work with real numbers but just rational numbers.

That is not the issue here -- after all, BigDecimal does precise 
arithmetic, but only with rational numbers.  The issue is rather that 
IEEE 754 does an inadequate job of representing arbitrary rational 
numbers, and the small errors are accumulated and magnified in 
calculations.

> 
> Cheers
> 
>   robert

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen@marnen.org
-- 
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