On Tue, 12 Oct 2010 12:35:24 -0700 (PDT)
cej38 <junkerme...@gmail.com> wrote:
> The more that I think about it, the more I would rather have a set of
> equalities that always work. float= was a good try.
Then you can't use floats.
As others have explained, floats are imprecise by nature, being
limited to finite binary fractions. To make matters worse, you don't
input the numbers in binary, but in decimal, which means most of the
fractions you can input can't be represented as a float - so you get
an approximation. Given that the numbers are "fuzzy", the concept of
equality also becomes "fuzzy" - whether two numbers are equal will
depend on the context. So you have to choose the equality that's
appropriate for the context.
If you want precise numbers, Clojure has three options:
1) If you can represent everything as integers, then BigInteger is
probably the easiest to use, with the obvious drawback that it can't
handle fractional values, nor can it represent as large a value as a
float since you run out of memory. Letting units represent 1/1000's:
user> (- 123050 123049)
1
2) If you're going to stay in the world of decimal fractions, use
BigDecimal. This has some of the problems of floats, but between
allowing arbitrary precision and the input representation matching the
internal representation, they're not nearly as obnoxious.
user> (- 12.305M 12.3049M)
0.0001M
3) Clojure's rationals let you represent all rational values, until
you run out of memory. If you want a decimal approximation after the
calculation is done, that's easy to get as well:
user> (- 12305/1000 123049/10000)
1/10000
user> (float (- 12305/1000 123049/10000))
1.0E-4
<mike
--
Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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