the world without the literal notation for floating-point numbers
DESCRIPTION
We need the decimal-point literal notation for Rational instead of Float because Float is legacy.TRANSCRIPT
The world without the literal notation for floating-point numbers
村田賢太, Kenta MurataGeneticLab Co., Ltd.
浮動小数点数リテラルが無い世界
1Tuesday, July 19, 2011
村田賢太 (mrkn)Kenta Murata
http://www.flickr.com/photos/koichiroo/5244581973/
CRuby Committer(BigDecimal)
Ruby Sapporo
Kosen Conf
2Tuesday, July 19, 2011
2010年3月1日月曜日 3Tuesday, July 19, 2011
2010年3月1日月曜日
ジュンク堂 RubyKaigi 支店残り n 冊!!
4Tuesday, July 19, 2011
札幌 Ruby 会議04
Sapporo RubyKaigi 04
Summer 2012
5Tuesday, July 19, 2011
I have some question.
6Tuesday, July 19, 2011
Do you use Float values?
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Do you understand Float well?
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Float is too difficult.
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Reading difficulty
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ruby-1.9.2-p290 :001 > 76287755398823936.0 => 76287755398823940.0 ruby-1.9.2-p290 :002 >
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Comparing difficulty
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ruby-1.9.2-p290 :001 > 12.4 * 1.05 == 13.02 => false
ruby-1.9.2-p290 :002 > 12.4 * 1.05 => 13.020000000000001 ruby-1.9.2-p290 :003 >
13Tuesday, July 19, 2011
Representation difference
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Human: Decimal
Internal: Binary
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Conceptdifference
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We think
Float is a number.
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It is real that
Float is a range.
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They’re troublesome
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There is a solution
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Why not use Rational.
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It is difficult, too.
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Ruby doesn’t haveany literal notations
for Rational
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Does a fractional notation solve the
problems?
24Tuesday, July 19, 2011
No!
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We naturally use decimal point notation.
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We need a decimal-point notation for
representing a Rational.
27Tuesday, July 19, 2011
ruby--p290 :001 > 13.02.class => Rational
ruby--p290 :001 > 12.4 * 1.05 == 13.02 => true
ruby-1.9.2-p290 :002 > 12.4 * 1.05 => 13.02
ruby-1.9.2-p290 :003 > 13.02 / 3 => (217/50)
28Tuesday, July 19, 2011
Do you worry about Rational is slow?
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We can optimize for denominators of 10n
30Tuesday, July 19, 2011
Float isn’t as so fast as you think
31Tuesday, July 19, 2011
If you need fast Float calculation
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Write it in C as extension library
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If you need to calculate with arrays of Float
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Use NArray
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Rational may bewhat you want
36Tuesday, July 19, 2011
This talk’s background, demonstrations, and
more detail descriptions
37Tuesday, July 19, 2011
38Tuesday, July 19, 2011