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In [[mathematics]], the '''limit inferior''' (also called '''infimum limit''', '''liminf''', '''inferior limit''', '''lower limit''', or '''inner limit''') and '''limit superior''' (also called '''supremum limit''', '''limit supremum''', '''limsup''', '''superior limit''', '''upper limit''', or '''outer limit''') of a [[sequence]] can be thought of as limiting (i.e., eventual and extreme) bounds on the sequence. The limit inferior and limit superior of a [[function (mathematics)|function]] can be thought of in a similar fashion (see [[limit of a function]]). The limit inferior and limit superior of a set are the [[infimum]] and [[supremum]] of the set's [[limit point]]s, respectively. 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.


[[Image:Lim sup example 5.png|right|thumb|300px|An illustration of limit superior and limit inferior. The sequence ''x''<sub>''n''</sub> is shown in blue. The two red curves approach the limit superior and limit inferior of ''x''<sub>''n''</sub>, shown as dashed black lines. In this case, the sequence ''accumulates'' around the two limits. The superior limit is the larger of the two, and the inferior limit is the smaller of the two. The inferior and superior limits agree if and only if the sequence is convergent (i.e., when there is a single limit).]]


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==Definition for sequences==
The limit inferior of a sequence (''x''<sub>''n''</sub>) is defined by
 
:<math>\liminf_{n\to\infty}x_n := \lim_{n\to\infty}\Big(\inf_{m\geq n}x_m\Big)</math>
 
or
 
:<math>\liminf_{n\to\infty}x_n := \sup_{n\geq 0}\,\inf_{m\geq n}x_m=\sup\{\,\inf\{\,x_m:m\geq n\,\}:n\geq 0\,\}.</math>
 
Similarly, the limit superior of (''x''<sub>''n''</sub>) is defined by
 
:<math>\limsup_{n\to\infty}x_n := \lim_{n\to\infty}\Big(\sup_{m\geq n}x_m\Big)</math>
 
or
 
:<math>\limsup_{n\to\infty}x_n := \inf_{n\geq 0}\,\sup_{m\geq n}x_m=\inf\{\,\sup\{\,x_m:m\geq n\,\}:n\geq 0\,\}.</math>
 
Alternatively, the notations <math>\varliminf_{n\to\infty}x_n:=\liminf_{n\to\infty}x_n</math> and <math>\varlimsup_{n\to\infty}x_n:=\limsup_{n\to\infty}x_n</math> are sometimes used.
 
If the terms in the sequence are real numbers, the limit superior and limit inferior always exist, as real numbers or ±∞ (i.e., on the [[extended real number line]]). More generally, these definitions make sense in any [[partially ordered set]], provided the [[supremum|suprema]] and [[infimum|infima]] exist, such as in a [[complete lattice]].
 
Whenever the ordinary limit exists, the limit inferior and limit superior are both equal to it; therefore, each can be considered a generalization of the ordinary limit which is primarily interesting in cases where the limit does ''not'' exist. Whenever lim inf ''x''<sub>''n''</sub> and lim sup ''x''<sub>''n''</sub> both exist, we have
 
:<math>\liminf_{n\to\infty}x_n\leq\limsup_{n\to\infty}x_n.</math>
 
Limits inferior/superior are related to [[big-O notation]] in that they bound a sequence only "in the limit"; the sequence may exceed the bound. However, with big-O notation the sequence can only exceed the bound in a finite prefix of the sequence, whereas the limit superior of a sequence like e<sup>-''n''</sup> may actually be less than all elements of the sequence. The only promise made is that some tail of the sequence can be bounded by the limit superior (inferior) plus (minus) an arbitrarily small positive constant.
 
The limit superior and limit inferior of a sequence are a special case of those of a function (see below).
 
== The case of sequences of real numbers ==
 
In [[mathematical analysis]], limit superior and limit inferior are important tools for studying sequences of [[real number]]s. Since the supremum and infimum of an unbounded set of real numbers may not exist (the reals are not a complete lattice), it is convenient to consider sequences in the [[affinely extended real number system]]: we add the positive and negative infinities to the real line to give the complete [[totally ordered set]] [-∞,∞], which is a complete lattice.
 
=== Interpretation ===
 
Consider a sequence <math>(x_n)</math> consisting of real numbers. Assume that the limit superior and limit inferior are real numbers (so, not infinite).
* The limit superior of <math>x_n</math> is the smallest real number <math>b</math> such that, for any positive real number <math>\varepsilon</math>, there exists a [[natural number]] <math>N</math> such that <math>x_n<b+\varepsilon</math> for all <math>n>N</math>. In other words, any number larger than the limit superior is an eventual upper bound for the sequence. Only a finite number of elements of the sequence are greater than <math>b+\varepsilon</math>.
* The limit inferior of <math>x_n</math> is the largest real number <math>b</math> that, for any positive real number <math>\varepsilon</math>, there exists a natural number <math>N</math> such that <math>x_n>b-\varepsilon</math> for all <math>n>N</math>. In other words, any number below the limit inferior is an eventual lower bound for the sequence. Only a finite number of elements of the sequence are less than <math>b-\varepsilon</math>.
 
=== Properties ===
 
The relationship of limit inferior and limit superior for sequences of real numbers is as follows
 
:<math>-\liminf_{n\to\infty} x_n = \limsup_{n\to\infty} (-x_n).</math>
 
As mentioned earlier, it is convenient to extend <math>\mathbb{R}</math> to [−∞,∞]. Then, (''x''<sub>''n''</sub>) in [−∞,∞] [[limit of a sequence|converges]] [[if and only if]]
 
:<math>\liminf_{n\to\infty} x_n = \limsup_{n\to\infty} x_n,</math>
 
in which case <math>\lim_{n\to\infty} x_n</math> is equal to their common value. (Note that when working just in <math>\mathbb{R}</math>, convergence to −∞ or ∞ would not be considered as convergence.) Since the limit inferior is at most the limit superior, the condition
 
:<math>\liminf_{n\to\infty} x_n = \infty</math>
 
implies that
 
:<math>\lim_{n\to\infty} x_n = \infty,</math>
 
and the condition
 
:<math>\limsup_{n\to\infty} x_n = - \infty</math>
 
implies that
 
:<math>\lim_{n\to\infty} x_n = - \infty.</math>
 
If
 
:<math>I = \liminf_{n\to\infty} x_n</math>
 
and
 
:<math>S = \limsup_{n\to\infty} x_n,</math>
 
then the interval [''I'', ''S''] need not contain any of the numbers ''x''<sub>''n''</sub>, but every slight enlargement [''I''&nbsp;&minus;&nbsp;ε, ''S''&nbsp;+&nbsp;ε] (for arbitrarily small ε > 0) will contain ''x''<sub>''n''</sub> for all but finitely many indices ''n''. In fact, the interval [''I'', ''S''] is the smallest closed interval with this property. We can formalize this property like this. If there exists a <math>\Lambda\in\mathbb{R}</math> so that
 
:<math>\Lambda<\limsup_{n\to\infty}x_n</math>
 
then there exists a [[subsequence]] <math>x_{k_n}</math> of <math>x_n</math> for which we have that
 
:<math>x_{k_n}>\Lambda\quad \forall n.</math>
 
In the same way, an analogous property holds for the limit inferior: if
 
:<math>\liminf_{n\to\infty}x_n<\lambda</math>
 
then there exists a subsequence <math>x_{k_n}</math> of <math>x_n</math> for which we have that
 
:<math>x_{k_n}<\lambda\quad\forall n.</math>
 
On the other hand we have that if
 
:<math>\limsup_{n\to\infty}x_n<\Lambda</math>
 
there exists a <math>n_0\in\mathbb{N}</math> so that
 
:<math>x_n<\Lambda\quad\forall n\geq n_0.</math>
 
Similarly, if there exists a <math>\lambda\in \mathbb{R}</math> so that
 
:<math>\lambda<\liminf_{n\to\infty}x_n</math>
 
there exists a <math>n_0\in\mathbb{N}</math> so that
 
:<math>x_n>\lambda\quad\forall n\geq n_0.</math>
 
To recapitulate:
 
* If <math>\Lambda</math> is greater than the limit superior, there are at most finitely many <math>x_n</math> greater than <math>\Lambda</math>; if it is less, there are infinitely many.
* If <math>\lambda</math> is less than the limit inferior, there are at most finitely many <math>x_n</math> less than <math>\lambda</math>; if it is greater, there are infinitely many.
 
In general we have that
 
:<math>\inf_n x_n \leq \liminf_{n \to \infty} x_n \leq \limsup_{n \to \infty} x_n \leq \sup_n x_n</math>
 
The liminf and limsup of a sequence are respectively the smallest and greatest [[Limit point|cluster points]].
 
* For any two sequences of real numbers <math>\{a_n\}, \{b_n\}</math>, the limit superior satisfies [[subadditivity]] whenever the right side of the inequality is defined (i.e., not <math>\infty - \infty</math> or <math>-\infty + \infty</math>):
:<math>\limsup_{n \to \infty} (a_n + b_n) \leq \limsup_{n \to \infty}(a_n) + \limsup_{n \to \infty}(b_n).</math>.
 
Analogously, the limit inferior satisfies [[superadditivity]]:
:<math>\liminf_{n \to \infty} (a_n + b_n) \geq \liminf_{n \to \infty}(a_n) + \liminf_{n \to \infty}(b_n).</math>
 
In the particular case that one of the sequences actually converges, say <math>a_n \to a </math>, then the inequalities above become equalities (with <math>\limsup_{n \to \infty}a_n</math> or <math>\liminf_{n \to \infty}a_n</math> being replaced by <math>a</math>).
 
==== Examples ====
 
* As an example, consider the sequence given by ''x''<sub>''n''</sub> = [[trigonometric function|sin]](''n''). Using the fact that [[pi]] is [[irrational number|irrational]], one can show that
:<math>\liminf_{n\to\infty} x_n = -1</math>
 
and
 
:<math>\limsup_{n\to\infty} x_n = +1.</math>
 
(This is because the sequence {1,2,3,...} is [[Equidistributed mod 1|equidistributed mod 2&pi;]], a consequence of the [[Equidistribution theorem]].)
 
* An example from [[number theory]] is
 
:<math>\liminf_{n\to\infty}(p_{n+1}-p_n),</math>
 
where ''p''<sub>''n''</sub> is the ''n''-th [[prime number]].
The value of this limit inferior is conjectured to be 2 - this is the [[twin prime conjecture]] - but has so far only been proven less than 70 million.<ref>{{cite web|last=Zhang|first=Yitang|title=Bounded gaps between primes|url=http://annals.math.princeton.edu/wp-content/uploads/YitangZhang.pdf|work=Annals of Mathematics|publisher=Princeton University|accessdate=28 May 2013}}</ref> The corresponding limit superior is <math>+\infty</math>, because there are arbitrary [[Gaps between prime numbers|gaps between consecutive primes]].
 
== Real-valued functions ==
 
Assume that a function is defined from a subset of the real numbers to the real numbers. As in the case for sequences, the limit inferior and limit superior are always well-defined if we allow the values +∞ and -∞; in fact, if both agree then the limit exists and is equal to their common value (again possibly including the infinities). For example, given ''f''(''x'') = sin(1/''x''), we have lim sup<sub>''x''→''0''</sub> ''f''(''x'') = 1 and lim inf<sub>''x''→''0''</sub> ''f''(''x'') = -1. The difference between the two is a rough measure of how "wildly" the function oscillates, and in observation of this fact, it is called the [[Oscillation (mathematics)|oscillation]] of ''f'' at ''a''. This idea of oscillation is sufficient to, for example, characterize [[Riemann integral|Riemann-integrable]] functions as continuous except on a set of [[measure zero]] [http://tt.lamf.uwindsor.ca/314folder/analbookfiles/RintexistLebesgue.pdf].  Note that points of nonzero oscillation (i.e., points at which ''f'' is "[[pathological (mathematics)|badly behaved]]") are discontinuities which, unless they make up a set of zero, are confined to a negligible set.
 
== Functions from metric spaces to metric spaces ==
 
There is a notion of lim sup and lim inf for functions defined on a [[metric space]] whose relationship to limits of real-valued functions mirrors that of the relation between the lim sup, lim inf, and the limit of a real sequence. Take metric spaces ''X'' and ''Y'', a subspace ''E'' contained in ''X'', and a function ''f''&nbsp;:&nbsp;''E''&nbsp;→&nbsp;''Y''.  The space ''Y'' should also be an [[Totally ordered set|ordered set]], so that the notions of supremum and infimum make sense.  Define, for any [[limit point]] ''a'' of ''E'',
 
:<math>\limsup_{x \to a} f(x) = \lim_{\varepsilon \to 0} ( \sup \{ f(x) : x \in E \cap B(a;\varepsilon) - \{a\} \} ) </math>
and
 
:<math>\liminf_{x \to a} f(x) = \lim_{\varepsilon \to 0} ( \inf \{ f(x) : x \in E \cap B(a;\varepsilon) - \{a\} \} ) </math>
 
where ''B''(''a'';ε) denotes the [[Ball (mathematics)|metric ball]] of radius ε about ''a''.
 
Note that as ε shrinks, the supremum of the function over the ball is monotone decreasing, so we have
 
:<math>\limsup_{x\to a} f(x)  = \inf_{\varepsilon > 0} (\sup \{ f(x) : x \in E \cap B(a;\varepsilon) - \{a\} \}) </math>
and similarly
:<math>\liminf_{x\to a} f(x) = \sup_{\varepsilon > 0}(\inf \{ f(x) : x \in E \cap B(a;\varepsilon) - \{a\} \}).</math>
 
This finally motivates the definitions for general topological spaces. Take ''X'', ''Y'', ''E'' and ''a'' as before, but now let ''X'' and ''Y'' both be topological spaces. In this case, we replace metric balls with neighborhoods:
 
:<math>\limsup_{x\to a} f(x) = \inf \{ \sup \{ f(x) : x \in E \cap U - \{a\} \} :  U\ \mathrm{open}, a \in U, E \cap U - \{a\} \neq \emptyset  \}</math>
:<math>\liminf_{x\to a} f(x) = \sup \{ \inf \{ f(x) : x \in E \cap U - \{a\} \} :  U\ \mathrm{open}, a \in U, E \cap U - \{a\} \neq \emptyset  \}</math>
 
(there is a way to write the formula using a ''lim'' using nets and the neighborhood filter). This version is often useful in discussions of [[semi-continuity]] which crop up in analysis quite often. An interesting note is that this version subsumes the sequential version by considering sequences as functions from the natural numbers as a topological subspace of the extended real line, into the space (the closure of '''N''' in [-∞, ∞] is '''N''' ∪ {∞}.)
 
== Sequences of sets ==
 
The [[power set]] ℘(''X'') of a [[Set (mathematics)|set]] ''X'' is a [[complete lattice]] that is ordered by [[inclusion (set theory)|set inclusion]], and so the supremum and infimum of any set of subsets (in terms of set inclusion) always exist. In particular, every subset ''Y'' of ''X'' is bounded above by ''X'' and below by the empty set ∅ because ∅ ⊆ ''Y'' ⊆ ''X''. Hence, it is possible (and sometimes useful) to consider superior and inferior limits of sequences in ℘(''X'') (i.e., sequences of subsets of ''X'').
 
There are two common ways to define the limit of sequences of sets. In both cases:
* The sequence ''accumulates'' around sets of points rather than single points themselves. That is, because each element of the sequence is itself a set, there exist accumulation ''sets'' that are somehow nearby to infinitely many elements of the sequence.
* The supremum/superior/outer limit is a set that [[join (mathematics)|join]]s these accumulation sets together. That is, it is the union of all of the accumulation sets. When ordering by set inclusion, the supremum limit is the least upper bound on the set of accumulation points because it ''contains'' each of them. Hence, it is the supremum of the limit points.
* The infimum/inferior/inner limit is a set where all of these accumulation sets [[meet (mathematics)|meet]]. That is, it is the intersection of all of the accumulation sets. When ordering by set inclusion, the infimum limit is the greatest lower bound on the set of accumulation points because it is ''contained in'' each of them. Hence, it is the infimum of the limit points.
* Because ordering is by set inclusion, then the outer limit will always contain the inner limit (i.e., lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> ⊆ lim&nbsp;sup&nbsp;''X''<sub>''n''</sub>). Hence, when considering the convergence of a sequence of sets, it generally suffices to consider the convergence of the outer limit of that sequence.
The difference between the two definitions involves the [[topology]] (i.e., how to quantify separation) is defined. In fact, the second definition is identical to the first when the [[discrete metric]] is used to induce the topology on ''X''.
 
===General set convergence===
 
In this case, a sequence of sets approaches a limiting set when the elements of each member of the sequence approach the elements of the limiting set. In particular, if {''X''<sub>''n''</sub>} is a sequence of subsets of ''X'', then:
* lim&nbsp;sup&nbsp;''X''<sub>''n''</sub>, which is also called the '''outer limit''', consists of those elements which are limits of points in ''X''<sub>''n''</sub> taken from [[countably infinite|(countably) infinite]]ly many ''n''. That is, ''x'' ∈ lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> if and only if there exists a sequence of points ''x''<sub>''k''</sub> and a ''subsequence'' {''X''<sub>''n''<sub>''k''</sub></sub>} of {''X''<sub>''n''</sub>} such that ''x''<sub>''k''</sub> ∈ ''X''<sub>''n''<sub>''k''</sub></sub> and ''x''<sub>''k''</sub> → ''x'' as ''k'' → ∞.
* lim&nbsp;inf&nbsp;''X''<sub>''n''</sub>, which is also called the '''inner limit''', consists of those elements which are limits of points in ''X''<sub>''n''</sub> for all but finitely many ''n'' (i.e., [[cofinitely]] many ''n''). That is, ''x'' ∈ lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> if and only if there exists a ''sequence'' of points {''x''<sub>''k''</sub>} such that ''x''<sub>''k''</sub> ∈ ''X''<sub>''k''</sub> and ''x''<sub>''k''</sub> → ''x'' as ''k'' → ∞.
The limit lim&nbsp;''X''<sub>''n''</sub> exists if and only if lim&nbsp;inf ''X''<sub>''n''</sub> and lim&nbsp;sup ''X''<sub>''n''</sub> agree, in which case lim&nbsp;''X''<sub>''n''</sub> = lim&nbsp;sup ''X''<sub>''n''</sub> = lim&nbsp;inf ''X''<sub>''n''</sub>.<ref name="GSTeel09">{{Cite journal
    |last1=Goebel
    |first1=Rafal
    |last2=Sanfelice
    |first2=Ricardo G.
    |last3=Teel
    |first3=Andrew R.
    |title=Hybrid dynamical systems
    |journal=IEEE Control Systems Magazine
    |year=2009
    |volume=29
    |issue=2
    |pages=28&ndash;93
    |doi=10.1109/MCS.2008.931718}}</ref>
 
===Special case: discrete metric===
 
In this case, which is frequently used in [[measure theory]], a sequence of sets approaches a limiting set when the limiting set includes elements from each of the members of the sequence. That is, this case specializes the first case when the topology on set ''X'' is induced from the [[discrete metric]]. For points ''x'' ∈ ''X'' and ''y'' ∈ ''X'', the discrete metric is defined by
:<math>d(x,y) := \begin{cases} 0 &\text{if } x = y,\\ 1 &\text{if } x \neq y. \end{cases}</math>
So a sequence of points {''x''<sub>''k''</sub>} converges to point ''x'' ∈ ''X'' if and only if ''x''<sub>''k''</sub> = ''x'' for all but finitely many ''k''. The following definition is the result of applying this metric to the general definition above.
 
If {''X''<sub>''n''</sub>} is a sequence of subsets of ''X'', then:
* lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> consists of elements of ''X'' which belong to ''X''<sub>''n''</sub> for '''infinitely many''' ''n'' (see [[countably infinite]]). That is, ''x'' ∈ lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> if and only if there exists a subsequence {''X''<sub>''n''<sub>''k''</sub></sub>} of {''X''<sub>''n''</sub>} such that ''x'' ∈ ''X''<sub>''n''<sub>''k''</sub></sub> for all ''k''.
* lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> consists of elements of ''X'' which belong to ''X''<sub>''n''</sub> for '''all but finitely many''' ''n'' (i.e., for [[cofinitely]] many ''n''). That is, ''x'' ∈ lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> if and only if there exists some ''m''>0 such that ''x'' ∈ ''X''<sub>''n''</sub> for all ''n''>''m''.
The limit lim&nbsp;''X'' exists if and only if lim&nbsp;inf ''X'' and lim&nbsp;sup ''X'' agree, in which case lim&nbsp;''X'' = lim&nbsp;sup ''X'' = lim&nbsp;inf ''X''.<ref name="Halmos50">{{Cite book
|title=Measure Theory
|last=Halmos
|first=Paul R.
|year=1950
|location=Princeton, NJ
|publisher=D. Van Nostrand Company, Inc.}}</ref> This definition of the inferior and superior limits is relatively strong because it requires that the elements of the extreme limits also be elements of each of the sets of the sequence.
 
Using the standard parlance of set theory, consider the infimum of a sequence of sets. The infimum is a greatest lower ''bound'' or [[meet (mathematics)|meet]] of a set. In the case of a sequence of sets, the sequence constituents meet at a set that is somehow smaller than each constituent set. [[inclusion (set theory)|Set inclusion]] provides an ordering that allows set intersection to generate a greatest lower bound ∩''X''<sub>''n''</sub> of sets in the sequence {''X''<sub>''n''</sub>}. Similarly, the supremum, which is the least upper bound or [[join (mathematics)|join]], of a sequence of sets is the union ∪''X''<sub>''n''</sub> of sets in sequence {''X''<sub>''n''</sub>}.
In this context, the inner limit lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> is the largest meeting of tails of the sequence, and the outer limit lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> is the smallest joining of tails of the sequence.
 
*Let ''I''<sub>''n''</sub> be the meet of the ''n''<sup>th</sup> tail of the sequence. That is,
::<math>I_n := \inf \{ X_m : m \in \{n, n+1, n+2, \ldots\}\} = \bigcap_{m=n}^{\infty} X_m = X_n \cap X_{n+1} \cap X_{n+2} \cap \cdots.</math>
:Then ''I''<sub>''k''</sub> &sube; ''I''<sub>''k''+1</sub> &sube; ''I''<sub>''k''+2</sub> because ''I''<sub>''k''+1</sub> is the intersection of fewer sets than ''I''<sub>''k''</sub>. In particular, the sequence {''I''<sub>''k''</sub>} is non-decreasing. So the inner/inferior limit is the least upper bound on this sequence of '''meets of tails'''. In particular,
::<math>\begin{align}
\liminf_{n\to\infty}X_n &:= \lim_{n\to\infty} \inf\{X_m: m \in \{n, n+1, \ldots\}\}\\
&= \sup\{\inf\{X_m: m \in \{n, n+1, \ldots\}\}: n \in \{1,2,\dots\}\}\\
&= {\bigcup_{n=1}^\infty}\left({\bigcap_{m=n}^\infty}X_m\right).
\end{align}</math>
:So the inferior limit acts like a version of the standard infimum that is unaffected by the set of elements that occur only finitely many times. That is, the infimum limit is a subset (i.e., a lower bound) for all but finitely many elements.
 
*Similarly, let ''J''<sub>''m''</sub> be the join of the ''m''<sup>th</sup> tail of the sequence. That is,
::<math>J_m := \sup \{ X_m : m \in \{n, n+1, n+2, \ldots\}\} = \bigcup_{m=n}^{\infty} X_m = X_n \cup X_{n+1} \cup X_{n+2} \cup \cdots.</math>
:Then ''J''<sub>''k''</sub> &supe; ''J''<sub>''k''+1</sub> &supe; ''J''<sub>''k''+2</sub> because ''J''<sub>''k''+1</sub> is the union of fewer sets than ''J''<sub>''k''</sub>. In particular, the sequence {''J''<sub>''k''</sub>} is non-increasing. So the outer/superior limit is the greatest lower bound on this sequence of '''joins of tails'''. In particular,
::<math>\begin{align}
\limsup_{n\to\infty}X_n &:= \lim_{n\to\infty} \sup\{X_m: m \in \{n, n+1, \ldots\}\}\\
&= \inf\{\sup\{X_m: m \in \{n, n+1, \ldots\}\}: n \in \{1,2,\dots\}\}\\
&= {\bigcap_{n=1}^\infty}\left({\bigcup_{m=n}^\infty}X_m\right).
\end{align}</math>
:So the superior limit acts like a version of the standard supremum that is unaffected by the set of elements that occur only finitely many times. That is, the supremum limit is a superset (i.e., an upper bound) for all but finitely many elements.
 
The limit lim&nbsp;''X''<sub>''n''</sub> exists if and only if lim&nbsp;sup&nbsp;''X''<sub>''n''</sub>=lim&nbsp;inf&nbsp;''X''<sub>''n''</sub>, and in that case, lim&nbsp;''X''<sub>''n''</sub>=lim&nbsp;inf&nbsp;''X''<sub>''n''</sub>=lim&nbsp;sup&nbsp;''X''<sub>''n''</sub>. In this sense, the sequence has a limit so long as all but finitely many of its elements are equal to the limit.
 
===Examples===
 
The following are several set convergence examples. They have been broken into sections with respect to the metric used to induce the topology on set ''X''.
 
; Using the [[discrete metric]]
 
* The [[Borel–Cantelli lemma]] is an example application of these constructs.
 
; Using either the discrete metric or the [[Euclidean metric]]
 
* Consider the set ''X'' = {0,1} and the sequence of subsets:
::<math>\{X_n\} = \{ \{0\},\{1\},\{0\},\{1\},\{0\},\{1\},\dots \}.</math>
:The "odd" and "even" elements of this sequence form two subsequences, <nowiki>{{</nowiki>0},{0},{0},...} and <nowiki>{{</nowiki>1},{1},{1},...}, which have limit points 0 and 1, respectively, and so the outer or superior limit is the set {0,1} of these two points. However, there are no limit points that can be taken from the {''X''<sub>''n''</sub>} sequence as a whole, and so the interior or inferior limit is the empty set {}. That is,
:* lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> = {0,1}
:* lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> = {}
:However, for {''Y''<sub>''n''</sub>} = <nowiki>{{</nowiki>0},{0},{0},...} and {''Z''<sub>''n''</sub>} = <nowiki>{{</nowiki>1},{1},{1},...}:
:* lim&nbsp;sup&nbsp;''Y''<sub>''n''</sub> = lim&nbsp;inf&nbsp;''Y''<sub>''n''</sub> = lim&nbsp;''Y''<sub>''n''</sub> = {0}
:* lim&nbsp;sup&nbsp;''Z''<sub>''n''</sub> = lim&nbsp;inf&nbsp;''Z''<sub>''n''</sub> = lim&nbsp;''Z''<sub>''n''</sub> = {1}
 
* Consider the set ''X'' = {50, 20, -100, -25, 0, 1} and the sequence of subsets:
::<math>\{X_n\} = \{ \{50\}, \{20\}, \{-100\}, \{-25\}, \{0\},\{1\},\{0\},\{1\},\{0\},\{1\},\dots \}.</math>
:As in the previous two examples,
:* lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> = {0,1}
:* lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> = {}
:That is, the four elements that do not match the pattern do not affect the lim&nbsp;inf and lim&nbsp;sup because there are only finitely many of them. In fact, these elements could be placed anywhere in the sequence (e.g., at positions 100, 150, 275, and 55000). So long as the ''tails'' of the sequence are maintained, the outer and inner limits will be unchanged. The related concepts of ''essential'' inner and outer limits, which use the [[essential supremum]] and [[essential infimum]], provide an important modification that "squashes" countably many (rather than just finitely many) interstitial additions.
 
; Using the Euclidean metric
 
* Consider the sequence of subsets of [[rational number]]s:
::<math>\{X_n\} = \{ \{0\},\{1\},\{1/2\},\{1/2\},\{2/3\},\{1/3\}, \{3/4\}, \{1/4\}, \dots \}.</math>
:The "odd" and "even" elements of this sequence form two subsequences, <nowiki>{{</nowiki>0},{1/2},{2/3},{3/4},...} and <nowiki>{{</nowiki>1},{1/2},{1/3},{1/4},...}, which have limit points 1 and 0, respectively, and so the outer or superior limit is the set {0,1} of these two points. However, there are no limit points that can be taken from the {''X''<sub>''n''</sub>} sequence as a whole, and so the interior or inferior limit is the empty set {}. So, as in the previous example,
:* lim&nbsp;sup&nbsp;''X''<sub>''n''</sub> = {0,1}
:* lim&nbsp;inf&nbsp;''X''<sub>''n''</sub> = {}
:However, for {''Y''<sub>''n''</sub>} = <nowiki>{{</nowiki>0},{1/2},{2/3},{3/4},...} and {''Z''<sub>''n''</sub>} = <nowiki>{{</nowiki>1},{1/2},{1/3},{1/4},...}:
:* lim&nbsp;sup&nbsp;''Y''<sub>''n''</sub> = lim&nbsp;inf&nbsp;''Y''<sub>''n''</sub> = lim&nbsp;''Y''<sub>''n''</sub> = {1}
:* lim&nbsp;sup&nbsp;''Z''<sub>''n''</sub> = lim&nbsp;inf&nbsp;''Z''<sub>''n''</sub> = lim&nbsp;''Z''<sub>''n''</sub> = {0}
:In each of these four cases, the elements of the limiting sets are not elements of any of the sets from the original sequence.
 
* The Ω limit (i.e., [[limit set]]) of a solution to a [[dynamic system]] is the outer limit of solution trajectories of the system.<ref name="GSTeel09"/>{{rp|50&ndash;51}} Because trajectories become closer and closer to this limit set, the tails of these trajectories ''converge'' to the limit set.
:* For example, an LTI system that is the [[cascade connection]] of several [[stability theory|stable]] systems with an undamped second-order [[LTI system]] (i.e., zero [[damping ratio]]) will oscillate endlessly after being perturbed (e.g., an ideal bell after being struck). Hence, if the position and velocity of this system are plotted against each other, trajectories will approach a circle in the [[state space (controls)|state space]]. This circle, which is the &Omega; limit set of the system, is the outer limit of solution trajectories of the system. The circle represents the locus of a trajectory corresponding to a pure sinusoidal tone output; that is, the system output approaches/approximates a pure tone.
 
==Generalized definitions==
 
The above definitions are inadequate for many technical applications. In fact, the definitions above are specializations of the following definitions.
 
===Definition for a set===
 
The limit inferior of a set ''X'' ⊆ ''Y'' is the [[infimum]] of all of the [[limit point]]s of the set. That is,
:<math>\liminf X := \inf \{ x \in Y : x \text{ is a limit point of } X \}\,</math>
Similarly, the limit superior of a set ''X'' is the [[supremum]] of all of the limit points of the set. That is,
:<math>\limsup X := \sup \{ x \in Y : x \text{ is a limit point of } X \}\,</math>
Note that the set ''X'' needs to be defined as a subset of a [[partially ordered set]] ''Y'' that is also a [[topological space]] in order for these definitions to make sense. Moreover, it has to be a [[complete lattice]] so that the suprema and infima always exist. In that case every set has a limit superior and a limit inferior. Also note that the limit inferior and the limit superior of a set do not have to be elements of the set.
 
===Definition for filter bases===
 
Take a [[topological space]] ''X'' and a [[filter base]] ''B'' in that space. The set of all [[cluster point]]s for that filter base is given by
:<math>\bigcap \{ \overline{B}_0 : B_0 \in B \}</math>
where <math>\overline{B}_0</math> is the [[closure (topology)|closure]] of <math>B_0</math>. This is clearly a [[closed set]] and is similar to the set of limit points of a set. Assume that ''X'' is also a [[partially ordered set]]. The limit superior of the filter base ''B'' is defined as
:<math>\limsup B := \sup \bigcap \{ \overline{B}_0 : B_0 \in B \}</math>
when that supremum exists. When ''X'' has a [[total order]], is a [[complete lattice]] and has the [[order topology]],
:<math>\limsup B = \inf\{ \sup B_0 : B_0 \in B \}</math>
Proof:
Similarly, the limit inferior of the filter base ''B'' is defined as
:<math>\liminf B := \inf \bigcap \{ \overline{B}_0 : B_0 \in B \}</math>
when that infimum exists; if ''X'' is totally ordered, is a complete lattice, and has the order topology, then
:<math>\liminf B = \sup\{ \inf B_0 : B_0 \in B \}</math>
 
If the limit inferior and limit superior agree, then there must be exactly one cluster point and the limit of the filter base is equal to this unique cluster point.
 
====Specialization for sequences and nets====
Note that filter bases are generalizations of [[net (mathematics)|nets]], which are generalizations of [[sequence]]s. Therefore, these definitions give the limit inferior and [[Net_(mathematics)#Limit_superior|limit superior]] of any net (and thus any sequence) as well. For example, take topological space <math>X</math> and the net <math>(x_\alpha)_{\alpha \in A}</math>, where <math>(A,{\leq})</math> is a [[directed set]] and <math>x_\alpha \in X</math> for all <math>\alpha \in A</math>. The filter base ("of tails") generated by this net is <math>B</math> defined by
:<math>B := \{ \{ x_\alpha : \alpha_0 \leq \alpha \} : \alpha_0 \in A \}.\,</math>
Therefore, the limit inferior and limit superior of the net are equal to the limit superior and limit inferior of <math>B</math> respectively. Similarly, for topological space <math>X</math>, take the sequence <math>(x_n)</math> where <math>x_n \in X</math> for any <math>n \in \mathbb{N}</math> with <math>\mathbb{N}</math> being the set of [[natural number]]s. The filter base ("of tails") generated by this sequence is <math>C</math> defined by
:<math>C := \{ \{ x_n : n_0 \leq n \} : n_0 \in \mathbb{N} \}.\,</math>
Therefore, the limit inferior and limit superior of the sequence are equal to the limit superior and limit inferior of <math>C</math> respectively.
 
==See also==
* [[Essential supremum and essential infimum]]
* [[Envelope (waves)]]
 
==References==
; In-line references
{{reflist}}
 
; General references
{{refbegin}}
*{{cite book
| last      = Amann
| first      = H.
| coauthors  = Escher, Joachim
| title      = Analysis
| publisher  = Basel; Boston: Birkhäuser
| year      = 2005
| pages      =
| isbn      = 0-8176-7153-6
}}
 
*{{cite book
| last      = González
| first      = Mario O
| title      = Classical complex analysis
| publisher  = New York: M. Dekker
| year      = 1991
| pages      =
| isbn      = 0-8247-8415-4
}}
{{refend}}
 
==External links==
* {{springer|title=Upper and lower limits|id=p/u095830}}
 
[[Category:Limits (mathematics)]]

Revision as of 11:00, 1 December 2013

In mathematics, the limit inferior (also called infimum limit, liminf, inferior limit, lower limit, or inner limit) and limit superior (also called supremum limit, limit supremum, limsup, superior limit, upper limit, or outer limit) of a sequence can be thought of as limiting (i.e., eventual and extreme) bounds on the sequence. The limit inferior and limit superior of a function can be thought of in a similar fashion (see limit of a function). The limit inferior and limit superior of a set are the infimum and supremum of the set's limit points, respectively. 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.

An illustration of limit superior and limit inferior. The sequence xn is shown in blue. The two red curves approach the limit superior and limit inferior of xn, shown as dashed black lines. In this case, the sequence accumulates around the two limits. The superior limit is the larger of the two, and the inferior limit is the smaller of the two. The inferior and superior limits agree if and only if the sequence is convergent (i.e., when there is a single limit).

Definition for sequences

The limit inferior of a sequence (xn) is defined by

or

Similarly, the limit superior of (xn) is defined by

or

Alternatively, the notations and are sometimes used.

If the terms in the sequence are real numbers, the limit superior and limit inferior always exist, as real numbers or ±∞ (i.e., on the extended real number line). More generally, these definitions make sense in any partially ordered set, provided the suprema and infima exist, such as in a complete lattice.

Whenever the ordinary limit exists, the limit inferior and limit superior are both equal to it; therefore, each can be considered a generalization of the ordinary limit which is primarily interesting in cases where the limit does not exist. Whenever lim inf xn and lim sup xn both exist, we have

Limits inferior/superior are related to big-O notation in that they bound a sequence only "in the limit"; the sequence may exceed the bound. However, with big-O notation the sequence can only exceed the bound in a finite prefix of the sequence, whereas the limit superior of a sequence like e-n may actually be less than all elements of the sequence. The only promise made is that some tail of the sequence can be bounded by the limit superior (inferior) plus (minus) an arbitrarily small positive constant.

The limit superior and limit inferior of a sequence are a special case of those of a function (see below).

The case of sequences of real numbers

In mathematical analysis, limit superior and limit inferior are important tools for studying sequences of real numbers. Since the supremum and infimum of an unbounded set of real numbers may not exist (the reals are not a complete lattice), it is convenient to consider sequences in the affinely extended real number system: we add the positive and negative infinities to the real line to give the complete totally ordered set [-∞,∞], which is a complete lattice.

Interpretation

Consider a sequence consisting of real numbers. Assume that the limit superior and limit inferior are real numbers (so, not infinite).

Properties

The relationship of limit inferior and limit superior for sequences of real numbers is as follows

As mentioned earlier, it is convenient to extend to [−∞,∞]. Then, (xn) in [−∞,∞] converges if and only if

in which case is equal to their common value. (Note that when working just in , convergence to −∞ or ∞ would not be considered as convergence.) Since the limit inferior is at most the limit superior, the condition

implies that

and the condition

implies that

If

and

then the interval [I, S] need not contain any of the numbers xn, but every slight enlargement [I − ε, S + ε] (for arbitrarily small ε > 0) will contain xn for all but finitely many indices n. In fact, the interval [I, S] is the smallest closed interval with this property. We can formalize this property like this. If there exists a so that

then there exists a subsequence of for which we have that

In the same way, an analogous property holds for the limit inferior: if

then there exists a subsequence of for which we have that

On the other hand we have that if

there exists a so that

Similarly, if there exists a so that

there exists a so that

To recapitulate:

In general we have that

The liminf and limsup of a sequence are respectively the smallest and greatest cluster points.

.

Analogously, the limit inferior satisfies superadditivity:

In the particular case that one of the sequences actually converges, say , then the inequalities above become equalities (with or being replaced by ).

Examples

  • As an example, consider the sequence given by xn = sin(n). Using the fact that pi is irrational, one can show that

and

(This is because the sequence {1,2,3,...} is equidistributed mod 2π, a consequence of the Equidistribution theorem.)

where pn is the n-th prime number. The value of this limit inferior is conjectured to be 2 - this is the twin prime conjecture - but has so far only been proven less than 70 million.[1] The corresponding limit superior is , because there are arbitrary gaps between consecutive primes.

Real-valued functions

Assume that a function is defined from a subset of the real numbers to the real numbers. As in the case for sequences, the limit inferior and limit superior are always well-defined if we allow the values +∞ and -∞; in fact, if both agree then the limit exists and is equal to their common value (again possibly including the infinities). For example, given f(x) = sin(1/x), we have lim supx0 f(x) = 1 and lim infx0 f(x) = -1. The difference between the two is a rough measure of how "wildly" the function oscillates, and in observation of this fact, it is called the oscillation of f at a. This idea of oscillation is sufficient to, for example, characterize Riemann-integrable functions as continuous except on a set of measure zero [1]. Note that points of nonzero oscillation (i.e., points at which f is "badly behaved") are discontinuities which, unless they make up a set of zero, are confined to a negligible set.

Functions from metric spaces to metric spaces

There is a notion of lim sup and lim inf for functions defined on a metric space whose relationship to limits of real-valued functions mirrors that of the relation between the lim sup, lim inf, and the limit of a real sequence. Take metric spaces X and Y, a subspace E contained in X, and a function f : E → Y. The space Y should also be an ordered set, so that the notions of supremum and infimum make sense. Define, for any limit point a of E,

and

where B(a;ε) denotes the metric ball of radius ε about a.

Note that as ε shrinks, the supremum of the function over the ball is monotone decreasing, so we have

and similarly

This finally motivates the definitions for general topological spaces. Take X, Y, E and a as before, but now let X and Y both be topological spaces. In this case, we replace metric balls with neighborhoods:

(there is a way to write the formula using a lim using nets and the neighborhood filter). This version is often useful in discussions of semi-continuity which crop up in analysis quite often. An interesting note is that this version subsumes the sequential version by considering sequences as functions from the natural numbers as a topological subspace of the extended real line, into the space (the closure of N in [-∞, ∞] is N ∪ {∞}.)

Sequences of sets

The power set ℘(X) of a set X is a complete lattice that is ordered by set inclusion, and so the supremum and infimum of any set of subsets (in terms of set inclusion) always exist. In particular, every subset Y of X is bounded above by X and below by the empty set ∅ because ∅ ⊆ YX. Hence, it is possible (and sometimes useful) to consider superior and inferior limits of sequences in ℘(X) (i.e., sequences of subsets of X).

There are two common ways to define the limit of sequences of sets. In both cases:

  • The sequence accumulates around sets of points rather than single points themselves. That is, because each element of the sequence is itself a set, there exist accumulation sets that are somehow nearby to infinitely many elements of the sequence.
  • The supremum/superior/outer limit is a set that joins these accumulation sets together. That is, it is the union of all of the accumulation sets. When ordering by set inclusion, the supremum limit is the least upper bound on the set of accumulation points because it contains each of them. Hence, it is the supremum of the limit points.
  • The infimum/inferior/inner limit is a set where all of these accumulation sets meet. That is, it is the intersection of all of the accumulation sets. When ordering by set inclusion, the infimum limit is the greatest lower bound on the set of accumulation points because it is contained in each of them. Hence, it is the infimum of the limit points.
  • Because ordering is by set inclusion, then the outer limit will always contain the inner limit (i.e., lim inf Xn ⊆ lim sup Xn). Hence, when considering the convergence of a sequence of sets, it generally suffices to consider the convergence of the outer limit of that sequence.

The difference between the two definitions involves the topology (i.e., how to quantify separation) is defined. In fact, the second definition is identical to the first when the discrete metric is used to induce the topology on X.

General set convergence

In this case, a sequence of sets approaches a limiting set when the elements of each member of the sequence approach the elements of the limiting set. In particular, if {Xn} is a sequence of subsets of X, then:

  • lim sup Xn, which is also called the outer limit, consists of those elements which are limits of points in Xn taken from (countably) infinitely many n. That is, x ∈ lim sup Xn if and only if there exists a sequence of points xk and a subsequence {Xnk} of {Xn} such that xkXnk and xkx as k → ∞.
  • lim inf Xn, which is also called the inner limit, consists of those elements which are limits of points in Xn for all but finitely many n (i.e., cofinitely many n). That is, x ∈ lim inf Xn if and only if there exists a sequence of points {xk} such that xkXk and xkx as k → ∞.

The limit lim Xn exists if and only if lim inf Xn and lim sup Xn agree, in which case lim Xn = lim sup Xn = lim inf Xn.[2]

Special case: discrete metric

In this case, which is frequently used in measure theory, a sequence of sets approaches a limiting set when the limiting set includes elements from each of the members of the sequence. That is, this case specializes the first case when the topology on set X is induced from the discrete metric. For points xX and yX, the discrete metric is defined by

So a sequence of points {xk} converges to point xX if and only if xk = x for all but finitely many k. The following definition is the result of applying this metric to the general definition above.

If {Xn} is a sequence of subsets of X, then:

  • lim sup Xn consists of elements of X which belong to Xn for infinitely many n (see countably infinite). That is, x ∈ lim sup Xn if and only if there exists a subsequence {Xnk} of {Xn} such that xXnk for all k.
  • lim inf Xn consists of elements of X which belong to Xn for all but finitely many n (i.e., for cofinitely many n). That is, x ∈ lim inf Xn if and only if there exists some m>0 such that xXn for all n>m.

The limit lim X exists if and only if lim inf X and lim sup X agree, in which case lim X = lim sup X = lim inf X.[3] This definition of the inferior and superior limits is relatively strong because it requires that the elements of the extreme limits also be elements of each of the sets of the sequence.

Using the standard parlance of set theory, consider the infimum of a sequence of sets. The infimum is a greatest lower bound or meet of a set. In the case of a sequence of sets, the sequence constituents meet at a set that is somehow smaller than each constituent set. Set inclusion provides an ordering that allows set intersection to generate a greatest lower bound ∩Xn of sets in the sequence {Xn}. Similarly, the supremum, which is the least upper bound or join, of a sequence of sets is the union ∪Xn of sets in sequence {Xn}. In this context, the inner limit lim inf Xn is the largest meeting of tails of the sequence, and the outer limit lim sup Xn is the smallest joining of tails of the sequence.

  • Let In be the meet of the nth tail of the sequence. That is,
Then IkIk+1Ik+2 because Ik+1 is the intersection of fewer sets than Ik. In particular, the sequence {Ik} is non-decreasing. So the inner/inferior limit is the least upper bound on this sequence of meets of tails. In particular,
So the inferior limit acts like a version of the standard infimum that is unaffected by the set of elements that occur only finitely many times. That is, the infimum limit is a subset (i.e., a lower bound) for all but finitely many elements.
  • Similarly, let Jm be the join of the mth tail of the sequence. That is,
Then JkJk+1Jk+2 because Jk+1 is the union of fewer sets than Jk. In particular, the sequence {Jk} is non-increasing. So the outer/superior limit is the greatest lower bound on this sequence of joins of tails. In particular,
So the superior limit acts like a version of the standard supremum that is unaffected by the set of elements that occur only finitely many times. That is, the supremum limit is a superset (i.e., an upper bound) for all but finitely many elements.

The limit lim Xn exists if and only if lim sup Xn=lim inf Xn, and in that case, lim Xn=lim inf Xn=lim sup Xn. In this sense, the sequence has a limit so long as all but finitely many of its elements are equal to the limit.

Examples

The following are several set convergence examples. They have been broken into sections with respect to the metric used to induce the topology on set X.

Using the discrete metric
Using either the discrete metric or the Euclidean metric
  • Consider the set X = {0,1} and the sequence of subsets:
The "odd" and "even" elements of this sequence form two subsequences, {{0},{0},{0},...} and {{1},{1},{1},...}, which have limit points 0 and 1, respectively, and so the outer or superior limit is the set {0,1} of these two points. However, there are no limit points that can be taken from the {Xn} sequence as a whole, and so the interior or inferior limit is the empty set {}. That is,
  • lim sup Xn = {0,1}
  • lim inf Xn = {}
However, for {Yn} = {{0},{0},{0},...} and {Zn} = {{1},{1},{1},...}:
  • lim sup Yn = lim inf Yn = lim Yn = {0}
  • lim sup Zn = lim inf Zn = lim Zn = {1}
  • Consider the set X = {50, 20, -100, -25, 0, 1} and the sequence of subsets:
As in the previous two examples,
  • lim sup Xn = {0,1}
  • lim inf Xn = {}
That is, the four elements that do not match the pattern do not affect the lim inf and lim sup because there are only finitely many of them. In fact, these elements could be placed anywhere in the sequence (e.g., at positions 100, 150, 275, and 55000). So long as the tails of the sequence are maintained, the outer and inner limits will be unchanged. The related concepts of essential inner and outer limits, which use the essential supremum and essential infimum, provide an important modification that "squashes" countably many (rather than just finitely many) interstitial additions.
Using the Euclidean metric
The "odd" and "even" elements of this sequence form two subsequences, {{0},{1/2},{2/3},{3/4},...} and {{1},{1/2},{1/3},{1/4},...}, which have limit points 1 and 0, respectively, and so the outer or superior limit is the set {0,1} of these two points. However, there are no limit points that can be taken from the {Xn} sequence as a whole, and so the interior or inferior limit is the empty set {}. So, as in the previous example,
  • lim sup Xn = {0,1}
  • lim inf Xn = {}
However, for {Yn} = {{0},{1/2},{2/3},{3/4},...} and {Zn} = {{1},{1/2},{1/3},{1/4},...}:
  • lim sup Yn = lim inf Yn = lim Yn = {1}
  • lim sup Zn = lim inf Zn = lim Zn = {0}
In each of these four cases, the elements of the limiting sets are not elements of any of the sets from the original sequence.
  • The Ω limit (i.e., limit set) of a solution to a dynamic system is the outer limit of solution trajectories of the system.[2]Primarily based on the most recent URA personal property value index (PPPI) flash estimates, we know that the PPPI, which represents the overall real property price development, has dipped in 2013Q4. That is the first dip the market has seen within the final 2 years.

    To give you some perspective, the entire number of personal properties in Singapore (together with govt condominiums) is 297,689 in 2013Q3. Primarily based on the projection that there will be 19,302 units accomplished in 2014, the rise in residential models works out to be more than 6%. With a lot New Ec Launch Singapore provide, buyers might be spoilt for alternative and this in flip will lead to their reluctance to pay a premium for potential models. The complete textual content of the Copyright Act (Cap sixty three) and different statutes regarding IPR might be found on the Singapore Statutes Online Website online The Group's income jumped forty.1 p.c to $324.5 million from $231.6 million in FY 2013, lifted by increased development income and sales of growth properties in Singapore and China. Actual Estate Shopping for

    One factor we've on this nation is a big group of "economists," and "market analysts." What's interesting about this group of real property market-watchers is that there are two very other ways wherein they predict Boomers will affect housing markets over the subsequent decade. Let's check out those two opposites and see how every can change the best way real property investors strategy their markets. The good news is that actual property buyers are prepared for either state of affairs, and there's profit in being ready. I'm excited and searching ahead to the alternatives both or each of these conditions will supply; thank you Boomers! Mapletree to further broaden past Asia Why fortune will favour the brave in Asia's closing real property frontier

    The story of the 23.2 home begins with a stack of Douglas fir beams salvaged from varied demolished warehouses owned by the consumer's household for a number of generations. Design and structure innovator Omer Arbel, configured them to type a triangulated roof, which makes up one of the placing features of the home. The transient from the entrepreneur-proprietor was not solely to design a house that integrates antique wood beams, however one which erases the excellence between inside and exterior. Built on a gentle slope on a large rural acreage surrounded by two masses of previous-development forests, the indoors movement seamlessly to the outdoors and, from the within looking, one enjoys unobstructed views of the existing natural panorama which is preserved

    First, there are typically extra rental transactions than gross sales transactions, to permit AV to be decided for each property primarily based on comparable properties. Second, movements in sale costs are more unstable than leases. Hence, utilizing rental transactions to derive the AV helps to maintain property tax more steady for property homeowners. If you're buying or trying to lease a property. It's tiring to call up individual property agent, organize appointments, coordinate timing and to go for particular person property viewing. What most individuals do is to have a property agent representing them who will arrange and coordinate the viewings for all the properties out there based mostly on your necessities & most well-liked timing. Rent Property District 12 Rent Property District thirteen

    The Annual Worth of a property is mostly derived based mostly on the estimated annual hire that it may well fetch if it have been rented out. In determining the Annual Worth of a property, IRAS will think about the leases of similar properties within the vicinity, dimension and condition of the property, and different relevant components. The Annual Worth of a property is determined in the identical method regardless of whether the property is let-out, proprietor-occupied or vacant. The Annual Worth of land is determined at 5% of the market price of the land. When a constructing is demolished, the Annual Worth of the land is assessed by this method. Property Tax on Residential Properties Buyer Stamp Responsibility on Buy of Properties – Business and residential properties Rent House District 01

    Within the event the Bank's valuation is decrease than the acquisition price, the purchaser has to pay the distinction between the purchase value and the Bank's valuation utilizing money. As such, the money required up-front might be increased so it's at all times essential to know the valuation of the property before making any offer. Appoint Lawyer The Bank will prepare for a proper valuation of the property by way of physical inspection The completion statement will present you the balance of the acquisition price that you must pay after deducting any deposit, pro-rated property tax and utility costs, upkeep prices, and different relevant expenses in addition to any fees payable to the agent and the lawyer. Stamp Responsibility Primarily based on the Purchase Price or Market Value, whichever is larger Because trajectories become closer and closer to this limit set, the tails of these trajectories converge to the limit set.
  • For example, an LTI system that is the cascade connection of several stable systems with an undamped second-order LTI system (i.e., zero damping ratio) will oscillate endlessly after being perturbed (e.g., an ideal bell after being struck). Hence, if the position and velocity of this system are plotted against each other, trajectories will approach a circle in the state space. This circle, which is the Ω limit set of the system, is the outer limit of solution trajectories of the system. The circle represents the locus of a trajectory corresponding to a pure sinusoidal tone output; that is, the system output approaches/approximates a pure tone.

Generalized definitions

The above definitions are inadequate for many technical applications. In fact, the definitions above are specializations of the following definitions.

Definition for a set

The limit inferior of a set XY is the infimum of all of the limit points of the set. That is,

Similarly, the limit superior of a set X is the supremum of all of the limit points of the set. That is,

Note that the set X needs to be defined as a subset of a partially ordered set Y that is also a topological space in order for these definitions to make sense. Moreover, it has to be a complete lattice so that the suprema and infima always exist. In that case every set has a limit superior and a limit inferior. Also note that the limit inferior and the limit superior of a set do not have to be elements of the set.

Definition for filter bases

Take a topological space X and a filter base B in that space. The set of all cluster points for that filter base is given by

where is the closure of . This is clearly a closed set and is similar to the set of limit points of a set. Assume that X is also a partially ordered set. The limit superior of the filter base B is defined as

when that supremum exists. When X has a total order, is a complete lattice and has the order topology,

Proof: Similarly, the limit inferior of the filter base B is defined as

when that infimum exists; if X is totally ordered, is a complete lattice, and has the order topology, then

If the limit inferior and limit superior agree, then there must be exactly one cluster point and the limit of the filter base is equal to this unique cluster point.

Specialization for sequences and nets

Note that filter bases are generalizations of nets, which are generalizations of sequences. Therefore, these definitions give the limit inferior and limit superior of any net (and thus any sequence) as well. For example, take topological space and the net , where is a directed set and for all . The filter base ("of tails") generated by this net is defined by

Therefore, the limit inferior and limit superior of the net are equal to the limit superior and limit inferior of respectively. Similarly, for topological space , take the sequence where for any with being the set of natural numbers. The filter base ("of tails") generated by this sequence is defined by

Therefore, the limit inferior and limit superior of the sequence are equal to the limit superior and limit inferior of respectively.

See also

References

In-line references

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.

General references

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  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534

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  • Other Sports Official Kull from Drumheller, has hobbies such as telescopes, property developers in singapore and crocheting. Identified some interesting places having spent 4 months at Saloum Delta.

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  2. 2.0 2.1 One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  3. 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534