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Correlation between $u$ and $partial_nu u$ on $partial Omega$ for a give PDE


Decompose solution of pde in harmonic and non-harmonic partOne problem about harmonic functionsWhat is precisely the definition of Elliptic Partial Differential Equation?Why $-int_{partial Omega }|u(x)|^2ds-int_Omega |nabla u|^2=0implies nabla u=0$?Prove that $|v|_{H^1(Omega )}leq C(|f|_{L^2(Omega )}+|v|_{H^{1/2}(partial Omega )}+|partial _nu v|_{H^{1/2}(partial Omega )}))$Prove $|v|_{H^1(Omega )}leq C(|f|_{L^2(Omega )}+|v|_{H^{1/2}(partial Omega )}+|partial _nu v|_{H^{-1/2}(partial Omega )})$Change of Variables for PDE posed in the bounded domain $Omega subset mathbb{R}^n$A bound for the PDE $frac{partial}{partial t}u=Delta u+ au$Critical points of solutions to PDEs on convex domainsA continuous extension operator $L^2(partial Omega) to H^1(Omega)$













1












$begingroup$


Given a bounded area $Omega subset mathbb{R}^n$ which is at least of class $C^3$. If now there is a function $u$ satisfying the PDE



begin{align*}
Delta u &= f~~~text{in }Omega \
u &= 0 ~~~text{in } partialOmega,
end{align*}

for some smooth function $f$. Is it then possible to show that $$partial_nu u overset{?}{=} 0$$
on $partial Omega$?










share|cite|improve this question











$endgroup$

















    1












    $begingroup$


    Given a bounded area $Omega subset mathbb{R}^n$ which is at least of class $C^3$. If now there is a function $u$ satisfying the PDE



    begin{align*}
    Delta u &= f~~~text{in }Omega \
    u &= 0 ~~~text{in } partialOmega,
    end{align*}

    for some smooth function $f$. Is it then possible to show that $$partial_nu u overset{?}{=} 0$$
    on $partial Omega$?










    share|cite|improve this question











    $endgroup$















      1












      1








      1


      1



      $begingroup$


      Given a bounded area $Omega subset mathbb{R}^n$ which is at least of class $C^3$. If now there is a function $u$ satisfying the PDE



      begin{align*}
      Delta u &= f~~~text{in }Omega \
      u &= 0 ~~~text{in } partialOmega,
      end{align*}

      for some smooth function $f$. Is it then possible to show that $$partial_nu u overset{?}{=} 0$$
      on $partial Omega$?










      share|cite|improve this question











      $endgroup$




      Given a bounded area $Omega subset mathbb{R}^n$ which is at least of class $C^3$. If now there is a function $u$ satisfying the PDE



      begin{align*}
      Delta u &= f~~~text{in }Omega \
      u &= 0 ~~~text{in } partialOmega,
      end{align*}

      for some smooth function $f$. Is it then possible to show that $$partial_nu u overset{?}{=} 0$$
      on $partial Omega$?







      real-analysis pde






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited 20 hours ago







      Bara

















      asked 20 hours ago









      BaraBara

      5510




      5510






















          1 Answer
          1






          active

          oldest

          votes


















          3












          $begingroup$

          It is not possible to show that result because it is in general not true. Think for instance in the PDE
          $$
          left{
          begin{array}{rl}
          -Delta u = 4,& textrm{in } Omega \
          u = 0,& textrm{on } partial Omega
          end{array}right.
          $$



          where $Omega={(x,y)in mathbb{R}^2: x^2+y^2 < 1}$.



          The exact solution is $u=1-x^2-y^2$, which does not have zero normal derivative on $partial Omega$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I guess you are missing "$<$" inside the definition of $Omega$.
            $endgroup$
            – GaC
            19 hours ago












          • $begingroup$
            Thanks, I'll correct it.
            $endgroup$
            – PierreCarre
            19 hours ago











          Your Answer





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          1 Answer
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          1 Answer
          1






          active

          oldest

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          active

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          active

          oldest

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          3












          $begingroup$

          It is not possible to show that result because it is in general not true. Think for instance in the PDE
          $$
          left{
          begin{array}{rl}
          -Delta u = 4,& textrm{in } Omega \
          u = 0,& textrm{on } partial Omega
          end{array}right.
          $$



          where $Omega={(x,y)in mathbb{R}^2: x^2+y^2 < 1}$.



          The exact solution is $u=1-x^2-y^2$, which does not have zero normal derivative on $partial Omega$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I guess you are missing "$<$" inside the definition of $Omega$.
            $endgroup$
            – GaC
            19 hours ago












          • $begingroup$
            Thanks, I'll correct it.
            $endgroup$
            – PierreCarre
            19 hours ago
















          3












          $begingroup$

          It is not possible to show that result because it is in general not true. Think for instance in the PDE
          $$
          left{
          begin{array}{rl}
          -Delta u = 4,& textrm{in } Omega \
          u = 0,& textrm{on } partial Omega
          end{array}right.
          $$



          where $Omega={(x,y)in mathbb{R}^2: x^2+y^2 < 1}$.



          The exact solution is $u=1-x^2-y^2$, which does not have zero normal derivative on $partial Omega$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            I guess you are missing "$<$" inside the definition of $Omega$.
            $endgroup$
            – GaC
            19 hours ago












          • $begingroup$
            Thanks, I'll correct it.
            $endgroup$
            – PierreCarre
            19 hours ago














          3












          3








          3





          $begingroup$

          It is not possible to show that result because it is in general not true. Think for instance in the PDE
          $$
          left{
          begin{array}{rl}
          -Delta u = 4,& textrm{in } Omega \
          u = 0,& textrm{on } partial Omega
          end{array}right.
          $$



          where $Omega={(x,y)in mathbb{R}^2: x^2+y^2 < 1}$.



          The exact solution is $u=1-x^2-y^2$, which does not have zero normal derivative on $partial Omega$.






          share|cite|improve this answer











          $endgroup$



          It is not possible to show that result because it is in general not true. Think for instance in the PDE
          $$
          left{
          begin{array}{rl}
          -Delta u = 4,& textrm{in } Omega \
          u = 0,& textrm{on } partial Omega
          end{array}right.
          $$



          where $Omega={(x,y)in mathbb{R}^2: x^2+y^2 < 1}$.



          The exact solution is $u=1-x^2-y^2$, which does not have zero normal derivative on $partial Omega$.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited 19 hours ago

























          answered 20 hours ago









          PierreCarrePierreCarre

          1,243211




          1,243211












          • $begingroup$
            I guess you are missing "$<$" inside the definition of $Omega$.
            $endgroup$
            – GaC
            19 hours ago












          • $begingroup$
            Thanks, I'll correct it.
            $endgroup$
            – PierreCarre
            19 hours ago


















          • $begingroup$
            I guess you are missing "$<$" inside the definition of $Omega$.
            $endgroup$
            – GaC
            19 hours ago












          • $begingroup$
            Thanks, I'll correct it.
            $endgroup$
            – PierreCarre
            19 hours ago
















          $begingroup$
          I guess you are missing "$<$" inside the definition of $Omega$.
          $endgroup$
          – GaC
          19 hours ago






          $begingroup$
          I guess you are missing "$<$" inside the definition of $Omega$.
          $endgroup$
          – GaC
          19 hours ago














          $begingroup$
          Thanks, I'll correct it.
          $endgroup$
          – PierreCarre
          19 hours ago




          $begingroup$
          Thanks, I'll correct it.
          $endgroup$
          – PierreCarre
          19 hours ago


















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