(definition)

**Definition:**
A theoretical measure of the execution of an *algorithm*, usually the time or memory needed, given the problem size n, which is usually the number of items. Informally, saying some equation f(n) = Ω (g(n)) means it is more than some constant multiple of g(n).

**Formal Definition:** f(n) = Ω (g(n)) means there are positive constants c and k, such that 0 ≤ cg(n) ≤ f(n) for all n ≥ k. The values of c and k must be fixed for the function f and must not depend on n.

**Generalization** (I am a kind of ...)

*big-O notation*.

**See also**
*ω(n)*.

*Note:
This is the upper-case Greek letter Omega. *

* This definition is stronger than the traditional mathematical definition. Here, f must be greater than g FOR ALL x bigger than some k. The traditional definition is f is big omega of g if it is not little o of g. That is, one needs only an unbounded sequence of values of x tending to infinity such that cg(x) ≤ f(x) for all x in the sequence. After Duncan Buell (BUELL@engr.sc.edu) 21 May 2004.*

Author: PEB

**Donald E. Knuth**, *Big Omicron and Big Omega and Big Theta*, SIGACT News, 8(2):18-24, April-June 1976.

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If you have suggestions, corrections, or comments, please get in touch with Paul Black.

Entry modified 5 March 2018.

HTML page formatted Wed Mar 13 12:42:45 2019.

Cite this as:

Paul E. Black, "Ω", in
*Dictionary of Algorithms and Data Structures* [online], Paul E. Black, ed. 5 March 2018. (accessed TODAY)
Available from: https://www.nist.gov/dads/HTML/omegaCapital.html