Lower limit of a real functionReal Analysis Monotone Convergence Theorem QuestionProve that $liminf x_n = -limsup (-x_n)$$X_nleq Y_n$ implies $liminf X_n leq liminf Y_n$ and $limsup X_n leq limsup Y_n$Show that if the sequence$(x_n)$ is bounded, then $(x_n)$ converges iff $limsup(x_n)=liminf(x_n)$.Limit of the sequence given by $x_n+1=x_n-x_n^n+1$If $a_n$ is bounded sequence , prove that $limsuplimits_nto infty a_n=-liminflimits_nto infty(-a_n)$Understanding the definitions of limit superior and limit inferior of a real sequenceLimit of square root of sequence given value of limit of original sequenceRequest for assistance on finishing the proof that $lim_ntoinftyn x_n = 0$ given some initial conditions.Upper Limit Definition

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Lower limit of a real function


Real Analysis Monotone Convergence Theorem QuestionProve that $liminf x_n = -limsup (-x_n)$$X_nleq Y_n$ implies $liminf X_n leq liminf Y_n$ and $limsup X_n leq limsup Y_n$Show that if the sequence$(x_n)$ is bounded, then $(x_n)$ converges iff $limsup(x_n)=liminf(x_n)$.Limit of the sequence given by $x_n+1=x_n-x_n^n+1$If $a_n$ is bounded sequence , prove that $limsuplimits_nto infty a_n=-liminflimits_nto infty(-a_n)$Understanding the definitions of limit superior and limit inferior of a real sequenceLimit of square root of sequence given value of limit of original sequenceRequest for assistance on finishing the proof that $lim_ntoinftyn x_n = 0$ given some initial conditions.Upper Limit Definition













0












$begingroup$



We define $f:X to Bbb R$ as a function, and $g: (0,1]to Bbb R$ defined by $$g(r) := inf_xin Br(x_0)f(x).$$
Denote $$
liminf_xto x_0f(x) := lim_rto 0^+g(r) = lim_rto 0^+inf_x∈Br(x_0)f(x).$$



i) Show that if $x_nto x_0$, then $liminflimits_nto inftyf(x_n) geq liminflimits_xto x_0 f(x)$.



ii) Show that there exists a sequence $x_n$ converging to $x_0$ such that $limlimits_nto inftyf(x_n) = liminflimits_xto x_0f(x).$




I have proven that limit of $g(r)$ as $r$ approaches $0$ exists and it is monotone decreasing. But I am confused as in isn't the definition of $liminflimits_xto x_0=inf liminflimits_nto infty f(x_n)$, which would prove both i) and ii) as trivial?










share|cite|improve this question











$endgroup$











  • $begingroup$
    My edit was for a minor typo.
    $endgroup$
    – DanielWainfleet
    21 hours ago










  • $begingroup$
    Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
    $endgroup$
    – DanielWainfleet
    21 hours ago















0












$begingroup$



We define $f:X to Bbb R$ as a function, and $g: (0,1]to Bbb R$ defined by $$g(r) := inf_xin Br(x_0)f(x).$$
Denote $$
liminf_xto x_0f(x) := lim_rto 0^+g(r) = lim_rto 0^+inf_x∈Br(x_0)f(x).$$



i) Show that if $x_nto x_0$, then $liminflimits_nto inftyf(x_n) geq liminflimits_xto x_0 f(x)$.



ii) Show that there exists a sequence $x_n$ converging to $x_0$ such that $limlimits_nto inftyf(x_n) = liminflimits_xto x_0f(x).$




I have proven that limit of $g(r)$ as $r$ approaches $0$ exists and it is monotone decreasing. But I am confused as in isn't the definition of $liminflimits_xto x_0=inf liminflimits_nto infty f(x_n)$, which would prove both i) and ii) as trivial?










share|cite|improve this question











$endgroup$











  • $begingroup$
    My edit was for a minor typo.
    $endgroup$
    – DanielWainfleet
    21 hours ago










  • $begingroup$
    Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
    $endgroup$
    – DanielWainfleet
    21 hours ago













0












0








0


1



$begingroup$



We define $f:X to Bbb R$ as a function, and $g: (0,1]to Bbb R$ defined by $$g(r) := inf_xin Br(x_0)f(x).$$
Denote $$
liminf_xto x_0f(x) := lim_rto 0^+g(r) = lim_rto 0^+inf_x∈Br(x_0)f(x).$$



i) Show that if $x_nto x_0$, then $liminflimits_nto inftyf(x_n) geq liminflimits_xto x_0 f(x)$.



ii) Show that there exists a sequence $x_n$ converging to $x_0$ such that $limlimits_nto inftyf(x_n) = liminflimits_xto x_0f(x).$




I have proven that limit of $g(r)$ as $r$ approaches $0$ exists and it is monotone decreasing. But I am confused as in isn't the definition of $liminflimits_xto x_0=inf liminflimits_nto infty f(x_n)$, which would prove both i) and ii) as trivial?










share|cite|improve this question











$endgroup$





We define $f:X to Bbb R$ as a function, and $g: (0,1]to Bbb R$ defined by $$g(r) := inf_xin Br(x_0)f(x).$$
Denote $$
liminf_xto x_0f(x) := lim_rto 0^+g(r) = lim_rto 0^+inf_x∈Br(x_0)f(x).$$



i) Show that if $x_nto x_0$, then $liminflimits_nto inftyf(x_n) geq liminflimits_xto x_0 f(x)$.



ii) Show that there exists a sequence $x_n$ converging to $x_0$ such that $limlimits_nto inftyf(x_n) = liminflimits_xto x_0f(x).$




I have proven that limit of $g(r)$ as $r$ approaches $0$ exists and it is monotone decreasing. But I am confused as in isn't the definition of $liminflimits_xto x_0=inf liminflimits_nto infty f(x_n)$, which would prove both i) and ii) as trivial?







real-analysis sequences-and-series limits






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited 21 hours ago









DanielWainfleet

35.7k31648




35.7k31648










asked yesterday









james blackjames black

419113




419113











  • $begingroup$
    My edit was for a minor typo.
    $endgroup$
    – DanielWainfleet
    21 hours ago










  • $begingroup$
    Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
    $endgroup$
    – DanielWainfleet
    21 hours ago
















  • $begingroup$
    My edit was for a minor typo.
    $endgroup$
    – DanielWainfleet
    21 hours ago










  • $begingroup$
    Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
    $endgroup$
    – DanielWainfleet
    21 hours ago















$begingroup$
My edit was for a minor typo.
$endgroup$
– DanielWainfleet
21 hours ago




$begingroup$
My edit was for a minor typo.
$endgroup$
– DanielWainfleet
21 hours ago












$begingroup$
Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
$endgroup$
– DanielWainfleet
21 hours ago




$begingroup$
Re: The last line. We have $lim inf_xto x_0f(x)=inf lim inf_nto inftyf(x_n): (x_n)_nin Bbb Nin S$ where $S$ is the set of $ all $ sequences that converge to $x_0$. There may be some $(x_n)_xin Bbb Nin S$ such that $lim inf_nto infty f(x_n)$ does not converge to $lim inf_xto x_0f(x)$. For example let $f(x)=1$ when $xin Bbb Q$ and $f(x)=0$ when $xnot in Bbb Q,$ and $x_0=0.$ Then $f(1/n)to 1$ as $nto infty$ but $lim inf_xto 0f(x)=0.$
$endgroup$
– DanielWainfleet
21 hours ago










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