Is $sqrt x$ locally Lipschitz continuous everywhere? The 2019 Stack Overflow Developer Survey...

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Is $sqrt x$ locally Lipschitz continuous everywhere?



The 2019 Stack Overflow Developer Survey Results Are InLocally Lipschitz and differentiable almost everywhereDifferentiable almost everywhere and LipschitzIs $sqrt{x}$ Lipschitz continuous on $(0,infty)$?Does global lipschitz imply locally lipschitz?Continuous and almost everywhere continuously differentiable with bounded gradient implies Lipschitz?Globally differentiable non-Lipschitz function that is uniformly continuous?Is a continuous and locally Lipschitz function Lipschitz?Concavity implies locally Lipschitz continuity?Property in-between Lipschitz continuous and *locally* Lipschitz continuous?Can a Lipschitz continuous function be linear almost everywhere but not linear everywhere?












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Is $f(x)=sqrt x$ locally Lipschitz continuous everywhere?



It is definitely not (globally) Lipschitz continuous. I wonder if it is locally Lipschitz continuous at $x=0$.










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$endgroup$

















    0












    $begingroup$


    Is $f(x)=sqrt x$ locally Lipschitz continuous everywhere?



    It is definitely not (globally) Lipschitz continuous. I wonder if it is locally Lipschitz continuous at $x=0$.










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      Is $f(x)=sqrt x$ locally Lipschitz continuous everywhere?



      It is definitely not (globally) Lipschitz continuous. I wonder if it is locally Lipschitz continuous at $x=0$.










      share|cite|improve this question











      $endgroup$




      Is $f(x)=sqrt x$ locally Lipschitz continuous everywhere?



      It is definitely not (globally) Lipschitz continuous. I wonder if it is locally Lipschitz continuous at $x=0$.







      real-analysis calculus functions continuity lipschitz-functions






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      share|cite|improve this question













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      edited Mar 21 at 5:15









      Ruslan

      3,73221634




      3,73221634










      asked Mar 21 at 5:03









      High GPAHigh GPA

      916422




      916422






















          1 Answer
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          3












          $begingroup$

          Hint: Consider any interval $[0,varepsilon)$ where $varepsilon > 0$. For $x,yin [0,varepsilon)$, with $x < y$, we have
          $$begin{align*}
          frac{|f(x)- f(y)|}{|x-y|} &= frac{sqrt{y} - sqrt{x}}{y - x}\
          &= frac{1}{sqrt{y}+sqrt{x}}.
          end{align*}$$
          Can you show that this can be made arbitrarily large, and if so, what can you conclude?






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
            $endgroup$
            – High GPA
            Mar 21 at 5:12






          • 1




            $begingroup$
            Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
            $endgroup$
            – Minus One-Twelfth
            Mar 21 at 5:15












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          1 Answer
          1






          active

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          active

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          votes









          3












          $begingroup$

          Hint: Consider any interval $[0,varepsilon)$ where $varepsilon > 0$. For $x,yin [0,varepsilon)$, with $x < y$, we have
          $$begin{align*}
          frac{|f(x)- f(y)|}{|x-y|} &= frac{sqrt{y} - sqrt{x}}{y - x}\
          &= frac{1}{sqrt{y}+sqrt{x}}.
          end{align*}$$
          Can you show that this can be made arbitrarily large, and if so, what can you conclude?






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
            $endgroup$
            – High GPA
            Mar 21 at 5:12






          • 1




            $begingroup$
            Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
            $endgroup$
            – Minus One-Twelfth
            Mar 21 at 5:15
















          3












          $begingroup$

          Hint: Consider any interval $[0,varepsilon)$ where $varepsilon > 0$. For $x,yin [0,varepsilon)$, with $x < y$, we have
          $$begin{align*}
          frac{|f(x)- f(y)|}{|x-y|} &= frac{sqrt{y} - sqrt{x}}{y - x}\
          &= frac{1}{sqrt{y}+sqrt{x}}.
          end{align*}$$
          Can you show that this can be made arbitrarily large, and if so, what can you conclude?






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
            $endgroup$
            – High GPA
            Mar 21 at 5:12






          • 1




            $begingroup$
            Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
            $endgroup$
            – Minus One-Twelfth
            Mar 21 at 5:15














          3












          3








          3





          $begingroup$

          Hint: Consider any interval $[0,varepsilon)$ where $varepsilon > 0$. For $x,yin [0,varepsilon)$, with $x < y$, we have
          $$begin{align*}
          frac{|f(x)- f(y)|}{|x-y|} &= frac{sqrt{y} - sqrt{x}}{y - x}\
          &= frac{1}{sqrt{y}+sqrt{x}}.
          end{align*}$$
          Can you show that this can be made arbitrarily large, and if so, what can you conclude?






          share|cite|improve this answer











          $endgroup$



          Hint: Consider any interval $[0,varepsilon)$ where $varepsilon > 0$. For $x,yin [0,varepsilon)$, with $x < y$, we have
          $$begin{align*}
          frac{|f(x)- f(y)|}{|x-y|} &= frac{sqrt{y} - sqrt{x}}{y - x}\
          &= frac{1}{sqrt{y}+sqrt{x}}.
          end{align*}$$
          Can you show that this can be made arbitrarily large, and if so, what can you conclude?







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Mar 21 at 5:12

























          answered Mar 21 at 5:09









          Minus One-TwelfthMinus One-Twelfth

          3,363413




          3,363413












          • $begingroup$
            My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
            $endgroup$
            – High GPA
            Mar 21 at 5:12






          • 1




            $begingroup$
            Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
            $endgroup$
            – Minus One-Twelfth
            Mar 21 at 5:15


















          • $begingroup$
            My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
            $endgroup$
            – High GPA
            Mar 21 at 5:12






          • 1




            $begingroup$
            Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
            $endgroup$
            – Minus One-Twelfth
            Mar 21 at 5:15
















          $begingroup$
          My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
          $endgroup$
          – High GPA
          Mar 21 at 5:12




          $begingroup$
          My guess: if we bound $x,yin[0,a]$ then the answer is "yes", so $f(x)$ is not locally lipschitz. If we bound $x,yin(0,a]$ then the answer is "no."
          $endgroup$
          – High GPA
          Mar 21 at 5:12




          1




          1




          $begingroup$
          Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
          $endgroup$
          – Minus One-Twelfth
          Mar 21 at 5:15




          $begingroup$
          Even if $x,y>0$, we can make $frac{1}{sqrt{y}+sqrt{x}}$ arbitrarily large. For example take $x= frac{1}{N+1}$ and $y = frac{1}{N}$ for some $N$ sufficiently large.
          $endgroup$
          – Minus One-Twelfth
          Mar 21 at 5:15


















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