# Supremum and infimum of a sequence for academic writing

In particular, a set can have many maximal and minimal elements, whereas infima and suprema are unique. If the supremum of a subset S exists, it is unique. However, if an infimum or supremum does exist, it is unique. Infima and suprema of real numbers[ edit ] In analysisinfima and suprema of subsets S of the real numbers are particularly important.

The two red curves approach the limit superior and limit inferior of xn, shown as dashed black lines. In a totally ordered set, like the real numbers, the concepts are the same. They can be thought of in a similar fashion for a function see limit of a function.

For instance, a lattice is a partially ordered set in which all nonempty finite subsets have both a supremum and an infimum, and a complete lattice is a partially ordered set in which all subsets have both a supremum and an infimum.

For example, it applies for real functions, and, since these can be considered special cases of functions, for real n-tuples and sequences of real numbers.

More information on the various classes of partially ordered sets that arise from such considerations are found in the article on completeness properties.

This set has a supremum but no greatest element.

Another example is the hyperreals ; there is no least upper bound of the set of positive infinitesimals. Limit inferior is also called infimum limit, limit infimum, liminf, inferior limit, lower limit, or inner limit; limit superior is also known as supremum limit, limit supremum, limsup, superior limit, upper limit, or outer limit.

An illustration of limit superior and limit inferior. In this case, the sequence accumulates around the two limits. In this case, it is also called the minimum of the set.

Consequently, partially ordered sets for which certain infima are known to exist become especially interesting. A well-ordered set also has the least-upper-bound property, and the empty subset has also a least upper bound: Existence and uniqueness[ edit ] Infima and suprema do not necessarily exist.

Hence, 0 is the least upper bound of the negative reals, so the supremum is 0. In mathematicsthe limit inferior and limit superior of a sequence can be thought of as limiting i. The limit inferior of a sequence x. The superior limit is the larger of the two, and the inferior limit is the smaller of the two.

If S contains a least element, then that element is the infimum; otherwise, the infimum does not belong to S or does not exist. Least-upper-bound property The least-upper-bound property is an example of the aforementioned completeness properties which is typical for the set of real numbers.

More generally, if a set has a smallest element, then the smallest element is the infimum for the set. This set has no greatest element, since for every element of the set, there is another, larger, element.

In general, when there are multiple objects around which a sequence, function, or set accumulates, the inferior and superior limits extract the smallest and largest of them; the type of object and the measure of size is context-dependent, but the notion of extreme limits is invariant.

If an ordered set S has the property that every nonempty subset of S having an upper bound also has a least upper bound, then S is said to have the least-upper-bound property.

Minimal upper bounds are those upper bounds for which there is no strictly smaller element that also is an upper bound. However, the definition of maximal and minimal elements is more general.

Relation to maximum and minimum elements[ edit ] The infimum of a subset S of a partially ordered set P, assuming it exists, does not necessarily belong to S. For instance, the negative real numbers do not have a greatest element, and their supremum is 0 which is not a negative real number.Infimum and supremum are very similar to minimum and maximum respectively, with a subtle difference.

Minimum and maximum of a set must always be attained, while there is. If the max exists, then it is the supremum. If the min exists, then it is the infimum. For an infinite set, it can happen that the max does not exist but the supremum does exist, and/or that the min does not exist but the infimum does exist.

In mathematics, the limit inferior and limit superior of a sequence can be thought of as limiting (i.e., eventual and extreme) bounds on the sequence. They can be thought of in a similar fashion for a function (see limit of a function).For a set, they are the infimum and supremum of the set's limit points, mi-centre.com general, when there are multiple objects around which a sequence.

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. The supremum (abbreviated sup; plural suprema) of a subset S of a partially ordered set T is the. Supremum and infimum We start with a straightforward definition similar to many others in this course.

Read the definitions carefully, and note the use of ⩽ and ⩾ here rather than. The supremum A non-empty set is bounded from above if there exists such that The number is called an upper bound of. If a set is bounded from above, then it has infinitely many upper bounds, because every number greater then the upper bound is also an upper bound.

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Supremum and infimum of a sequence for academic writing
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