 Big omega notation

For real-valued functions on the natural numbers, $f(n)=\Omega (g(n))$ means that constants $c>0$ and $N$ satisfy $|f(n)|\ge c|g(n)|$ for every $n\ge N$. This is an eventual lower bound on magnitude. In algorithm analysis the functions are usually nonnegative, so the absolute values can be omitted. Together with the upper bound of big O notation, it gives big theta notation. This is the algorithmic lower-bound convention for $\Omega$, rather than a convention expressing only a positive limit superior along a subsequence.