What's that CS "big word" term for the same action always having the same effect

Question

There's a computer science term for this that escapes my head, one of those words that ends with "-icity".

It means something like a given action will always produce the same result, IE there won't be any hysteresis, or the action will not alter the functioning of the system...

Ring a bell, anyone? Thanks.

_{Apologies for the tagging, I'm only tagging it Java b/c I learned about this in a Java class back in school and I figure that crowd tends to have more CS background...}

I think he means the word for a function that always returns the same result, given the same parameters (ex. sqrt). I cannot remember the word either... It is used in compiler optimization theory, it's not *'deterministic'* or *'idempotent'* though. — BlueRaja - Danny Pflughoeft, Jan 19 '10 at 21:11
Or since he mentioned hysteresis, he might be thinking of atomicity. A little help, OP? — BlueRaja - Danny Pflughoeft, Jan 19 '10 at 21:17
@BlueRaja: what you describe is a *pure function*: http://en.wikipedia.org/wiki/Pure_function — Stephan202, Jan 19 '10 at 21:20
@Stephan: Yes, that is it. For some reason, I remember my compiler professor calling it something else.. — BlueRaja - Danny Pflughoeft, Jan 19 '10 at 21:22
@BlueRaja: ...which is in turn related to Referential transparency (http://en.wikipedia.org/wiki/Referential_transparency_%28computer_science%29) and indeed compiler optimization theory. — Stephan202, Jan 19 '10 at 21:23
The Java crowd "tends to have more CS background" than who? Not my experience at all, by the way... — Drew Hall, Jan 19 '10 at 21:58

Dafydd Rees · Accepted Answer · 2012-04-30T21:19:47.980

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This could mean two different things:

deterministic - meaning that given the same initial state, the same operation (with exactly the same data) will always produce the same resulting state (and optional output.) - http://en.wikipedia.org/wiki/Deterministic_algorithm

i.e. same action has the same effect - assuming you start from the same place in the same system. (Nothing random about it, nothing fed in from the outside that could effect the result...)

idempotent - meaning applying a function to a value once e.g. f(x) = v produces the same result as applying the function multiple times e.g. f(f(f(x))) = v - http://en.wikipedia.org/wiki/Idempotence

i.e. one or more function applications yields the same value given the same initial value

edited Apr 30 '12 at 21:19

answered Jan 19 '10 at 21:07

Dafydd Rees

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I though deterministic just mens it does not crash :-) given the same starting state and input. (Joking) – Martin York Jan 20 '10 at 16:14
Yes! I was looking for idempotent - I guess it's not exactly what I thought it meant though, thanks! – ambertch Jan 21 '10 at 00:42
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for example, some light switches are idempotent, some are not. If you flip it up to turn it on, and flip it up again, it stays on, that's idempotent. If you press it to turn it on, then press it again, it turns off - that's not idempotent. – ja. Apr 28 '10 at 18:13

score 11 · Answer 2 · answered Jan 19 '10 at 21:06

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you mean idempotent ??

answered Jan 19 '10 at 21:06

ram

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That has to do with side effects, but not necessarily that it gives the same result. – troelskn Jan 20 '10 at 18:41
from wikipedia:Idempotence (pronounced /ˌaɪdɨmˈpoʊtəns/) describes the property of operations in mathematics and computer science that means that multiple applications of the operation do not change the result. – ram Jan 20 '10 at 18:44

score 11 · Answer 3 · answered Jan 19 '10 at 21:08

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Referential transparency is also used in some CS circles.

answered Jan 19 '10 at 21:08

Daniel

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score 8 · Answer 4 · answered Jan 19 '10 at 21:06

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Nullipotent?

answered Jan 19 '10 at 21:06

Platinum Azure

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This is the one that fits the criteria of the question. +1 – Hogan Jan 19 '10 at 21:18
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I guess to really fit the question you have to say Nullipotenticity – Hogan Jan 19 '10 at 21:19
Ahaha, true. I'm too lazy to edit, though, do forgive me. :-) – Platinum Azure Jan 19 '10 at 21:53

score 6 · Answer 5 · answered Jan 19 '10 at 21:04

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deterministic ,.,-=

answered Jan 19 '10 at 21:04

jspcal

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Deterministic still may alter the system. `myAccount.balance += 50` would deterministically withdraw money from account ;-) – notnoop Jan 19 '10 at 21:08
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I'd like to be able to withdrawal money while increasing my balance! – Ruddy Jan 19 '10 at 21:11

score 6 · Answer 6 · answered Jan 19 '10 at 21:37

Are you looking for invariant?

http://en.wikipedia.org/wiki/Invariant_%28computer_science%29

In computer science, a predicate is called an invariant to a sequence of operations if the predicate always evaluates at the end of the sequence to the same value as before starting the sequence.

score 4 · Answer 7 · answered Jan 19 '10 at 21:31

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side effect-free?

answered Jan 19 '10 at 21:31

Brian Postow

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score 3 · Answer 8 · answered Jan 19 '10 at 21:07

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In math, a function 'f' is idempotent if multiple applications do not change the result.

answered Jan 19 '10 at 21:07

Michael Easter

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score 2 · Answer 9 · answered Jan 19 '10 at 21:06

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you mean idempotence?

answered Jan 19 '10 at 21:06

Mauricio

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score 1 · Answer 10 · answered Jan 19 '10 at 21:06

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or the action will not alter the functioning of the system...

Are you looking for ‘idempotence’?

answered Jan 19 '10 at 21:06

bobince

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score 1 · Answer 11 · edited Feb 08 '17 at 14:19

The "ends with -icity" part of your question makes me think you might be looking for monotonicity, even though it does not quite match description/definition of the word. From the Wikipedia article:

In mathematics, a monotonic function (or monotone function) is a function which preserves the given order. This concept first arose in calculus, and was later generalized to the more abstract setting of order theory.

In the following illustrations (also borrowed from the Wikipedia article) three functions are drawn:

A: B: C:

A and B and both monotonic (increasing and decreasing respectively), while C is not monotonic.

score 0 · Answer 12 · answered Jan 19 '10 at 21:04

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You mean an atomic block of code?

answered Jan 19 '10 at 21:04

Terje

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score 0 · Answer 13 · answered Jan 19 '10 at 21:11

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The A in ACID.

Atomicity - states that database modifications must follow an “all or nothing” rule. Each transaction is said to be “atomic.” If one part of the transaction fails, the entire transaction fails.

answered Jan 19 '10 at 21:11

Yada

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score 0 · Answer 14 · answered Jan 19 '10 at 21:23

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It sounds like what you're describing would be a memoryless function. Although the term memorylessness is usually used for stochastic distributions, I don't quite remember if it has a programming equivalent...

answered Jan 19 '10 at 21:23

Wim

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What's that CS "big word" term for the same action always having the same effect

14 Answers14