Convergence of Bounded Variation on Open Subsets












4












$begingroup$


I was reading a proof in Evan's Measure Theory and he stated a lemma without proof that I cannot justify: Let $U$ be an open connected subset of $mathbb{R}^n$




Let $U_k := {x in U,|, text{dist}(x, partial Omega) > frac{1}{k} cap B_k(0)}$ where $B_k(0)$ is the ball of radius $k$ centered at $0$. Then $$
||Df||(U) := sup left{int_{U} f mathrm{ div } varphi; |; varphi in C_c^{infty}(U), |varphi| leq 1right };text{ implies };||Df||(U-U_k) rightarrow 0.
$$




It is easy to verify this for $f in W^{1,1}(U)$ since we have
$$
||Df||(U) = int_{U} |f'| dx.
$$

But for the general case, I'm having problems verifying this lemma. Any help would be appreciated.










share|cite|improve this question











$endgroup$

















    4












    $begingroup$


    I was reading a proof in Evan's Measure Theory and he stated a lemma without proof that I cannot justify: Let $U$ be an open connected subset of $mathbb{R}^n$




    Let $U_k := {x in U,|, text{dist}(x, partial Omega) > frac{1}{k} cap B_k(0)}$ where $B_k(0)$ is the ball of radius $k$ centered at $0$. Then $$
    ||Df||(U) := sup left{int_{U} f mathrm{ div } varphi; |; varphi in C_c^{infty}(U), |varphi| leq 1right };text{ implies };||Df||(U-U_k) rightarrow 0.
    $$




    It is easy to verify this for $f in W^{1,1}(U)$ since we have
    $$
    ||Df||(U) = int_{U} |f'| dx.
    $$

    But for the general case, I'm having problems verifying this lemma. Any help would be appreciated.










    share|cite|improve this question











    $endgroup$















      4












      4








      4





      $begingroup$


      I was reading a proof in Evan's Measure Theory and he stated a lemma without proof that I cannot justify: Let $U$ be an open connected subset of $mathbb{R}^n$




      Let $U_k := {x in U,|, text{dist}(x, partial Omega) > frac{1}{k} cap B_k(0)}$ where $B_k(0)$ is the ball of radius $k$ centered at $0$. Then $$
      ||Df||(U) := sup left{int_{U} f mathrm{ div } varphi; |; varphi in C_c^{infty}(U), |varphi| leq 1right };text{ implies };||Df||(U-U_k) rightarrow 0.
      $$




      It is easy to verify this for $f in W^{1,1}(U)$ since we have
      $$
      ||Df||(U) = int_{U} |f'| dx.
      $$

      But for the general case, I'm having problems verifying this lemma. Any help would be appreciated.










      share|cite|improve this question











      $endgroup$




      I was reading a proof in Evan's Measure Theory and he stated a lemma without proof that I cannot justify: Let $U$ be an open connected subset of $mathbb{R}^n$




      Let $U_k := {x in U,|, text{dist}(x, partial Omega) > frac{1}{k} cap B_k(0)}$ where $B_k(0)$ is the ball of radius $k$ centered at $0$. Then $$
      ||Df||(U) := sup left{int_{U} f mathrm{ div } varphi; |; varphi in C_c^{infty}(U), |varphi| leq 1right };text{ implies };||Df||(U-U_k) rightarrow 0.
      $$




      It is easy to verify this for $f in W^{1,1}(U)$ since we have
      $$
      ||Df||(U) = int_{U} |f'| dx.
      $$

      But for the general case, I'm having problems verifying this lemma. Any help would be appreciated.







      real-analysis measure-theory bounded-variation






      share|cite|improve this question















      share|cite|improve this question













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      edited Jan 26 at 7:35









      Daniele Tampieri

      2,3272922




      2,3272922










      asked Jan 23 at 11:19









      User12335425User12335425

      211




      211






















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