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When writing software, there are often situations where I need a parameter to be a floating point number $x \in [0,1]$. I don't know of a name for that category, but I think there must be one because it's such a useful categories. Perhaps there's a name in probability theory?

(If they don't have a name, I hereby declare them to be "wombat numbers".)

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    It's just the closed interval [0,1]2010-08-14
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    (tongue-in-cheek) Since there's no such thing as "irrational" or "transcendental" in floating-point... maybe "proper fractions"?2010-08-15
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    Just a curiosity: In Romanian they are sometimes called subunitary numbers (although it sometimes means in [-1,1]). Apparently in English "subunitary" is reserved for matrices.2010-08-15
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    Not sure I've seen "subunitary" in use, but "unitary" is indeed an adjective frequently used in the theory of matrices.2010-08-15
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    I'm running into the same question wrt probability numbers. Since all of the "official" answers seem to be multiword ("property fraction", "unit interval"), I'm going to go ahead and accept your declaration of "wombat" numbers, with my code reading getFloat(), getInt(), getWombat().2013-09-22

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Sometimes I've heard it called the "unit interval" as it "probability measures are functions from a boolean algebra to the unit interval"

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    I'd imagine the 'unit interval' refers to the set [0,1], but you wouldn't say that the number 0.3 is a "unit interval number" in the same way that you might say that 2/3 is a "rational number". It's not entirely clear from the question but I think it's asking for a term to describe any number in the set, not to describe the set itself.2010-08-15
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    "Numbers in the unit interval" works.2010-08-15
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    Thank you very much. Now I don't have to name my function "parseNumberBetweenZeroAndOne".2010-08-15
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    You should still call your function parseWombatNumbers. Semantic function names are for wimps. All my functions are called "foo78" "bar429" and so on2010-08-16
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    @Seamus To the contrary, naming things is [one of the hard problems](http://martinfowler.com/bliki/TwoHardThings.html). Only wimps give up on meaningful names. ;)2014-02-14
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I guess you could call them fractional numbers. But that might be a bit confusing :)

Another option would be "fuzzy truthvalue" or "fuzzy boolean".