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In mathematics, the infimum (abbreviated inf; plural infima) of a subset S of a partially ordered set T is the greatest element in T that is less than or equal to all elements of S, if such an element exists. Consequently, the term greatest lower bound (abbreviated as GLB) is also commonly used.
Formal definition
A lower bound of a subset S of a partially ordered set (P,≤) is an element a of P such that
a ≤ x for all x in S.
A lower bound a of S is called an infimum (or greatest lower bound, or meet) of S if
for all lower bounds y of S in P, y ≤ a (a is larger than any other lower bound).
최대, 최소와의 관련성을 따지자면 꼭 set 에 포함되지 않아도 된다.
The infimum of a subset S of a partially ordered set P, assuming it exists, does not necessarily belong to S.
예를들면,
Infima
The infimum of the set of numbers {2,3,4} is 2. The number 1 is a lower bound, but not the greatest lo wer bound, and hence not the infimum.
More generally, if a set has a smallest element, then the smallest element is the infimum for the set. In this case, it is also called the minimum of the set.
inf{1,2,3,...} = 1
inf{x∈R|0 inf{x∈Q|x^3 > 2} = cube root 2 inf{(-1)^n + 1/n | n = 1,2,3, ... } = -1 if X_n is a decresing sequence with limit x, then inf X_n = X.