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Solvability of Neumann problem


Analytical solution of Partial Differential EquationSmooth solutions of the Laplace equation with Neumann dataDoes the following have a solution for f(x,y)?How to show that a delta function solution to a PDE (Fokker-Planck) is really a solutionReformulate this PDE in different notationPoisson equation with nonlinear Neumann conditionsMethod of characteristics for a parabolic PDEDiscrete Neumann problem: Representation by Simple Random WalkDirichlet plus Neumann problem without a PDEUniqueness of solution for Dirichlet and Neumann problem













1












$begingroup$


Let $D$ be the domain in $mathbbR^2$ such that $x^2 + y^2 <4$ , and $alpha, beta$ and $ gamma $ be real constants. For which values of these three constants there is no solution for:$$Delta u =0 , (x,y)in D$$
$$partial_n u= alpha x^2 + beta y + gamma, (x,y) in partial D$$
How to solve the equation for the values of these three constants which the solution exists?



Thanks.










share|cite|improve this question









$endgroup$
















    1












    $begingroup$


    Let $D$ be the domain in $mathbbR^2$ such that $x^2 + y^2 <4$ , and $alpha, beta$ and $ gamma $ be real constants. For which values of these three constants there is no solution for:$$Delta u =0 , (x,y)in D$$
    $$partial_n u= alpha x^2 + beta y + gamma, (x,y) in partial D$$
    How to solve the equation for the values of these three constants which the solution exists?



    Thanks.










    share|cite|improve this question









    $endgroup$














      1












      1








      1


      1



      $begingroup$


      Let $D$ be the domain in $mathbbR^2$ such that $x^2 + y^2 <4$ , and $alpha, beta$ and $ gamma $ be real constants. For which values of these three constants there is no solution for:$$Delta u =0 , (x,y)in D$$
      $$partial_n u= alpha x^2 + beta y + gamma, (x,y) in partial D$$
      How to solve the equation for the values of these three constants which the solution exists?



      Thanks.










      share|cite|improve this question









      $endgroup$




      Let $D$ be the domain in $mathbbR^2$ such that $x^2 + y^2 <4$ , and $alpha, beta$ and $ gamma $ be real constants. For which values of these three constants there is no solution for:$$Delta u =0 , (x,y)in D$$
      $$partial_n u= alpha x^2 + beta y + gamma, (x,y) in partial D$$
      How to solve the equation for the values of these three constants which the solution exists?



      Thanks.







      pde






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked 2 days ago









      Math LoverMath Lover

      938




      938




















          2 Answers
          2






          active

          oldest

          votes


















          2












          $begingroup$

          In polar coordinates $(x,y) = (rcosphi,rsinphi)$ the general solution (which is finite at $r=0$) is



          $$ u(r,phi) = A_0 + sum_n=1^infty r^n big[A_ncos(nphi) + B_nsin(nphi)big] $$



          where $D = 0<r < 2$. The gradient is



          $$ u_r(r,phi) = alpha r^2cos^2phi + beta rsin(phi) + gamma = fracalpha r^22big[cos(2phi) + 1big] + beta r sin(phi) + gamma $$



          Evaluated at the boundary:



          $$ u_r(2,phi) = 2alphacos(2phi) + 2beta sin(phi) + (2alpha + gamma) $$



          You also have, from the general solution



          $$ u_r(2,phi) = sum_n=1^infty n2^n-1big[A_ncos(nphi) + B_nsin(phi)big] $$



          Comparing coefficients gives



          begincases
          2alpha + gamma = 0 \
          B_1 = 2beta \
          4A_2 = 2alpha
          endcases



          The first condition is required for the solution to exist.






          share|cite|improve this answer









          $endgroup$




















            0












            $begingroup$

            The Neumann problem has a solution iff $int_Sfdsigma=0$ , where $S$, is the circle with center the origin and radius $2$ and $f(x,y)=alpha x^2 + beta y + gamma$ . A parametrization for this circle is $(2cost, 2sint)$. Now if we take the above mentioned line - integral we get the desired condition: $2a+gamma=0$.



            Edit The proposition above is






            share|cite|improve this answer











            $endgroup$












            • $begingroup$
              What is $f$? ---
              $endgroup$
              – Dylan
              2 days ago










            • $begingroup$
              @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
              $endgroup$
              – dmtri
              2 days ago










            • $begingroup$
              It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
              $endgroup$
              – Dylan
              2 days ago










            • $begingroup$
              Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
              $endgroup$
              – dmtri
              2 days ago










            Your Answer





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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            2












            $begingroup$

            In polar coordinates $(x,y) = (rcosphi,rsinphi)$ the general solution (which is finite at $r=0$) is



            $$ u(r,phi) = A_0 + sum_n=1^infty r^n big[A_ncos(nphi) + B_nsin(nphi)big] $$



            where $D = 0<r < 2$. The gradient is



            $$ u_r(r,phi) = alpha r^2cos^2phi + beta rsin(phi) + gamma = fracalpha r^22big[cos(2phi) + 1big] + beta r sin(phi) + gamma $$



            Evaluated at the boundary:



            $$ u_r(2,phi) = 2alphacos(2phi) + 2beta sin(phi) + (2alpha + gamma) $$



            You also have, from the general solution



            $$ u_r(2,phi) = sum_n=1^infty n2^n-1big[A_ncos(nphi) + B_nsin(phi)big] $$



            Comparing coefficients gives



            begincases
            2alpha + gamma = 0 \
            B_1 = 2beta \
            4A_2 = 2alpha
            endcases



            The first condition is required for the solution to exist.






            share|cite|improve this answer









            $endgroup$

















              2












              $begingroup$

              In polar coordinates $(x,y) = (rcosphi,rsinphi)$ the general solution (which is finite at $r=0$) is



              $$ u(r,phi) = A_0 + sum_n=1^infty r^n big[A_ncos(nphi) + B_nsin(nphi)big] $$



              where $D = 0<r < 2$. The gradient is



              $$ u_r(r,phi) = alpha r^2cos^2phi + beta rsin(phi) + gamma = fracalpha r^22big[cos(2phi) + 1big] + beta r sin(phi) + gamma $$



              Evaluated at the boundary:



              $$ u_r(2,phi) = 2alphacos(2phi) + 2beta sin(phi) + (2alpha + gamma) $$



              You also have, from the general solution



              $$ u_r(2,phi) = sum_n=1^infty n2^n-1big[A_ncos(nphi) + B_nsin(phi)big] $$



              Comparing coefficients gives



              begincases
              2alpha + gamma = 0 \
              B_1 = 2beta \
              4A_2 = 2alpha
              endcases



              The first condition is required for the solution to exist.






              share|cite|improve this answer









              $endgroup$















                2












                2








                2





                $begingroup$

                In polar coordinates $(x,y) = (rcosphi,rsinphi)$ the general solution (which is finite at $r=0$) is



                $$ u(r,phi) = A_0 + sum_n=1^infty r^n big[A_ncos(nphi) + B_nsin(nphi)big] $$



                where $D = 0<r < 2$. The gradient is



                $$ u_r(r,phi) = alpha r^2cos^2phi + beta rsin(phi) + gamma = fracalpha r^22big[cos(2phi) + 1big] + beta r sin(phi) + gamma $$



                Evaluated at the boundary:



                $$ u_r(2,phi) = 2alphacos(2phi) + 2beta sin(phi) + (2alpha + gamma) $$



                You also have, from the general solution



                $$ u_r(2,phi) = sum_n=1^infty n2^n-1big[A_ncos(nphi) + B_nsin(phi)big] $$



                Comparing coefficients gives



                begincases
                2alpha + gamma = 0 \
                B_1 = 2beta \
                4A_2 = 2alpha
                endcases



                The first condition is required for the solution to exist.






                share|cite|improve this answer









                $endgroup$



                In polar coordinates $(x,y) = (rcosphi,rsinphi)$ the general solution (which is finite at $r=0$) is



                $$ u(r,phi) = A_0 + sum_n=1^infty r^n big[A_ncos(nphi) + B_nsin(nphi)big] $$



                where $D = 0<r < 2$. The gradient is



                $$ u_r(r,phi) = alpha r^2cos^2phi + beta rsin(phi) + gamma = fracalpha r^22big[cos(2phi) + 1big] + beta r sin(phi) + gamma $$



                Evaluated at the boundary:



                $$ u_r(2,phi) = 2alphacos(2phi) + 2beta sin(phi) + (2alpha + gamma) $$



                You also have, from the general solution



                $$ u_r(2,phi) = sum_n=1^infty n2^n-1big[A_ncos(nphi) + B_nsin(phi)big] $$



                Comparing coefficients gives



                begincases
                2alpha + gamma = 0 \
                B_1 = 2beta \
                4A_2 = 2alpha
                endcases



                The first condition is required for the solution to exist.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 2 days ago









                DylanDylan

                13.8k31027




                13.8k31027





















                    0












                    $begingroup$

                    The Neumann problem has a solution iff $int_Sfdsigma=0$ , where $S$, is the circle with center the origin and radius $2$ and $f(x,y)=alpha x^2 + beta y + gamma$ . A parametrization for this circle is $(2cost, 2sint)$. Now if we take the above mentioned line - integral we get the desired condition: $2a+gamma=0$.



                    Edit The proposition above is






                    share|cite|improve this answer











                    $endgroup$












                    • $begingroup$
                      What is $f$? ---
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                      $endgroup$
                      – dmtri
                      2 days ago










                    • $begingroup$
                      It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                      $endgroup$
                      – dmtri
                      2 days ago















                    0












                    $begingroup$

                    The Neumann problem has a solution iff $int_Sfdsigma=0$ , where $S$, is the circle with center the origin and radius $2$ and $f(x,y)=alpha x^2 + beta y + gamma$ . A parametrization for this circle is $(2cost, 2sint)$. Now if we take the above mentioned line - integral we get the desired condition: $2a+gamma=0$.



                    Edit The proposition above is






                    share|cite|improve this answer











                    $endgroup$












                    • $begingroup$
                      What is $f$? ---
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                      $endgroup$
                      – dmtri
                      2 days ago










                    • $begingroup$
                      It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                      $endgroup$
                      – dmtri
                      2 days ago













                    0












                    0








                    0





                    $begingroup$

                    The Neumann problem has a solution iff $int_Sfdsigma=0$ , where $S$, is the circle with center the origin and radius $2$ and $f(x,y)=alpha x^2 + beta y + gamma$ . A parametrization for this circle is $(2cost, 2sint)$. Now if we take the above mentioned line - integral we get the desired condition: $2a+gamma=0$.



                    Edit The proposition above is






                    share|cite|improve this answer











                    $endgroup$



                    The Neumann problem has a solution iff $int_Sfdsigma=0$ , where $S$, is the circle with center the origin and radius $2$ and $f(x,y)=alpha x^2 + beta y + gamma$ . A parametrization for this circle is $(2cost, 2sint)$. Now if we take the above mentioned line - integral we get the desired condition: $2a+gamma=0$.



                    Edit The proposition above is







                    share|cite|improve this answer














                    share|cite|improve this answer



                    share|cite|improve this answer








                    edited 2 days ago

























                    answered 2 days ago









                    dmtridmtri

                    1,6082521




                    1,6082521











                    • $begingroup$
                      What is $f$? ---
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                      $endgroup$
                      – dmtri
                      2 days ago










                    • $begingroup$
                      It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                      $endgroup$
                      – dmtri
                      2 days ago
















                    • $begingroup$
                      What is $f$? ---
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                      $endgroup$
                      – dmtri
                      2 days ago










                    • $begingroup$
                      It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                      $endgroup$
                      – Dylan
                      2 days ago










                    • $begingroup$
                      Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                      $endgroup$
                      – dmtri
                      2 days ago















                    $begingroup$
                    What is $f$? ---
                    $endgroup$
                    – Dylan
                    2 days ago




                    $begingroup$
                    What is $f$? ---
                    $endgroup$
                    – Dylan
                    2 days ago












                    $begingroup$
                    @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                    $endgroup$
                    – dmtri
                    2 days ago




                    $begingroup$
                    @Dylan, $f(x,y)=alpha x^2 + beta y + gamma$
                    $endgroup$
                    – dmtri
                    2 days ago












                    $begingroup$
                    It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                    $endgroup$
                    – Dylan
                    2 days ago




                    $begingroup$
                    It would help to specify that in your answer. Also mention which theorem this came from. This is a good answer but needs some more context.
                    $endgroup$
                    – Dylan
                    2 days ago












                    $begingroup$
                    Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                    $endgroup$
                    – dmtri
                    2 days ago




                    $begingroup$
                    Ok, thanks. See please "Introduction to PDE with Applications", by Zachamanoglou and Toe. It is just a ref in page 259 , line 14. Potential Theory is used here.
                    $endgroup$
                    – dmtri
                    2 days ago

















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