Prove that $||f||_p=sup|int fg dmu|$ The 2019 Stack Overflow Developer Survey Results Are InAn exercise in Rudin's RCAProve that lim sup $a_n$ $leq$ lim sup $b_n$.If $big|int gvarphi , dmubig|le Mintlvertvarphirvert,dmu,$ for all simple functions $varphi,,$ then $lvert grvert le M,$ a. e.Show that $sup f_n = sup g_n$ almost everywhere.Real Analysis, Folland Problem 6.2.17 Dual of $L^p$Does functions in $L^p(mathbbR)$ vanish outside of a set of finite measure?Fatou's Lemma Proof MisunderstandingProve that $sup(S)leqsup(T)$ and $inf(T)leqinf(S)$Show that $sup(S)=inf(T)$.Given $mu$ is semifinite and $mu(E)=infty$, prove that if $C>0$, then $exists$ measurable set $A subseteq E$ such that $C < mu(A) < infty.$

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Prove that $||f||_p=sup|int fg dmu|$



The 2019 Stack Overflow Developer Survey Results Are InAn exercise in Rudin's RCAProve that lim sup $a_n$ $leq$ lim sup $b_n$.If $big|int gvarphi , dmubig|le Mintlvertvarphirvert,dmu,$ for all simple functions $varphi,,$ then $lvert grvert le M,$ a. e.Show that $sup f_n = sup g_n$ almost everywhere.Real Analysis, Folland Problem 6.2.17 Dual of $L^p$Does functions in $L^p(mathbbR)$ vanish outside of a set of finite measure?Fatou's Lemma Proof MisunderstandingProve that $sup(S)leqsup(T)$ and $inf(T)leqinf(S)$Show that $sup(S)=inf(T)$.Given $mu$ is semifinite and $mu(E)=infty$, prove that if $C>0$, then $exists$ measurable set $A subseteq E$ such that $C < mu(A) < infty.$










0












$begingroup$


Let $mu$ be a $sigma$-finite measure and $1leq pleqinfty$,show that $||f||_p=sup|int fg dmu|$ where the supremum is taken over all bounded measurable functions $g$ that vanish outside a set (depending on $g$) of finite measure, and for which $||g||_p^primeleq 1$, ($p^prime$ is exponent conjugate of $p$) and $int fgdmu$
exists.










share|cite|improve this question









$endgroup$
















    0












    $begingroup$


    Let $mu$ be a $sigma$-finite measure and $1leq pleqinfty$,show that $||f||_p=sup|int fg dmu|$ where the supremum is taken over all bounded measurable functions $g$ that vanish outside a set (depending on $g$) of finite measure, and for which $||g||_p^primeleq 1$, ($p^prime$ is exponent conjugate of $p$) and $int fgdmu$
    exists.










    share|cite|improve this question









    $endgroup$














      0












      0








      0





      $begingroup$


      Let $mu$ be a $sigma$-finite measure and $1leq pleqinfty$,show that $||f||_p=sup|int fg dmu|$ where the supremum is taken over all bounded measurable functions $g$ that vanish outside a set (depending on $g$) of finite measure, and for which $||g||_p^primeleq 1$, ($p^prime$ is exponent conjugate of $p$) and $int fgdmu$
      exists.










      share|cite|improve this question









      $endgroup$




      Let $mu$ be a $sigma$-finite measure and $1leq pleqinfty$,show that $||f||_p=sup|int fg dmu|$ where the supremum is taken over all bounded measurable functions $g$ that vanish outside a set (depending on $g$) of finite measure, and for which $||g||_p^primeleq 1$, ($p^prime$ is exponent conjugate of $p$) and $int fgdmu$
      exists.







      real-analysis analysis






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Mar 24 at 4:14









      ZoeZoe

      134




      134




















          1 Answer
          1






          active

          oldest

          votes


















          0












          $begingroup$

          For $p>1$ : choose sets $A_n$ of finite measure increasing to $X$. LHS $leq$ RHS is immediate form Holder's inequality. Now consider $g=frac 1 c I_A_n |f|^p-1 sgn(f) I_x:$ where $c=(int_x: I_A_n |f|^p)^1/p'$. you can see that RHS $
          geq int fg$
          for each $N$ and tends to LHS as $N to infty$. [$sgn(f)$ stands for sign of $f$].
          I will let you handle the case $p=1$






          share|cite|improve this answer











          $endgroup$












          • $begingroup$
            But, where uses the assumption $mu$ is $sigma$-finite?
            $endgroup$
            – Zoe
            Mar 24 at 5:13










          • $begingroup$
            This approach still holds when the case $||f||_p=infty$?
            $endgroup$
            – Zoe
            Mar 24 at 5:21










          • $begingroup$
            @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 5:30










          • $begingroup$
            Thinks, now I think I can finish proof for the the case p=1
            $endgroup$
            – Zoe
            Mar 24 at 5:34











          Your Answer





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          1 Answer
          1






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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          0












          $begingroup$

          For $p>1$ : choose sets $A_n$ of finite measure increasing to $X$. LHS $leq$ RHS is immediate form Holder's inequality. Now consider $g=frac 1 c I_A_n |f|^p-1 sgn(f) I_x:$ where $c=(int_x: I_A_n |f|^p)^1/p'$. you can see that RHS $
          geq int fg$
          for each $N$ and tends to LHS as $N to infty$. [$sgn(f)$ stands for sign of $f$].
          I will let you handle the case $p=1$






          share|cite|improve this answer











          $endgroup$












          • $begingroup$
            But, where uses the assumption $mu$ is $sigma$-finite?
            $endgroup$
            – Zoe
            Mar 24 at 5:13










          • $begingroup$
            This approach still holds when the case $||f||_p=infty$?
            $endgroup$
            – Zoe
            Mar 24 at 5:21










          • $begingroup$
            @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 5:30










          • $begingroup$
            Thinks, now I think I can finish proof for the the case p=1
            $endgroup$
            – Zoe
            Mar 24 at 5:34















          0












          $begingroup$

          For $p>1$ : choose sets $A_n$ of finite measure increasing to $X$. LHS $leq$ RHS is immediate form Holder's inequality. Now consider $g=frac 1 c I_A_n |f|^p-1 sgn(f) I_x:$ where $c=(int_x: I_A_n |f|^p)^1/p'$. you can see that RHS $
          geq int fg$
          for each $N$ and tends to LHS as $N to infty$. [$sgn(f)$ stands for sign of $f$].
          I will let you handle the case $p=1$






          share|cite|improve this answer











          $endgroup$












          • $begingroup$
            But, where uses the assumption $mu$ is $sigma$-finite?
            $endgroup$
            – Zoe
            Mar 24 at 5:13










          • $begingroup$
            This approach still holds when the case $||f||_p=infty$?
            $endgroup$
            – Zoe
            Mar 24 at 5:21










          • $begingroup$
            @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 5:30










          • $begingroup$
            Thinks, now I think I can finish proof for the the case p=1
            $endgroup$
            – Zoe
            Mar 24 at 5:34













          0












          0








          0





          $begingroup$

          For $p>1$ : choose sets $A_n$ of finite measure increasing to $X$. LHS $leq$ RHS is immediate form Holder's inequality. Now consider $g=frac 1 c I_A_n |f|^p-1 sgn(f) I_x:$ where $c=(int_x: I_A_n |f|^p)^1/p'$. you can see that RHS $
          geq int fg$
          for each $N$ and tends to LHS as $N to infty$. [$sgn(f)$ stands for sign of $f$].
          I will let you handle the case $p=1$






          share|cite|improve this answer











          $endgroup$



          For $p>1$ : choose sets $A_n$ of finite measure increasing to $X$. LHS $leq$ RHS is immediate form Holder's inequality. Now consider $g=frac 1 c I_A_n |f|^p-1 sgn(f) I_x:$ where $c=(int_x: I_A_n |f|^p)^1/p'$. you can see that RHS $
          geq int fg$
          for each $N$ and tends to LHS as $N to infty$. [$sgn(f)$ stands for sign of $f$].
          I will let you handle the case $p=1$







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Mar 24 at 5:27

























          answered Mar 24 at 5:10









          Kavi Rama MurthyKavi Rama Murthy

          74.1k53270




          74.1k53270











          • $begingroup$
            But, where uses the assumption $mu$ is $sigma$-finite?
            $endgroup$
            – Zoe
            Mar 24 at 5:13










          • $begingroup$
            This approach still holds when the case $||f||_p=infty$?
            $endgroup$
            – Zoe
            Mar 24 at 5:21










          • $begingroup$
            @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 5:30










          • $begingroup$
            Thinks, now I think I can finish proof for the the case p=1
            $endgroup$
            – Zoe
            Mar 24 at 5:34
















          • $begingroup$
            But, where uses the assumption $mu$ is $sigma$-finite?
            $endgroup$
            – Zoe
            Mar 24 at 5:13










          • $begingroup$
            This approach still holds when the case $||f||_p=infty$?
            $endgroup$
            – Zoe
            Mar 24 at 5:21










          • $begingroup$
            @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
            $endgroup$
            – Kavi Rama Murthy
            Mar 24 at 5:30










          • $begingroup$
            Thinks, now I think I can finish proof for the the case p=1
            $endgroup$
            – Zoe
            Mar 24 at 5:34















          $begingroup$
          But, where uses the assumption $mu$ is $sigma$-finite?
          $endgroup$
          – Zoe
          Mar 24 at 5:13




          $begingroup$
          But, where uses the assumption $mu$ is $sigma$-finite?
          $endgroup$
          – Zoe
          Mar 24 at 5:13












          $begingroup$
          This approach still holds when the case $||f||_p=infty$?
          $endgroup$
          – Zoe
          Mar 24 at 5:21




          $begingroup$
          This approach still holds when the case $||f||_p=infty$?
          $endgroup$
          – Zoe
          Mar 24 at 5:21












          $begingroup$
          @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
          $endgroup$
          – Kavi Rama Murthy
          Mar 24 at 5:30




          $begingroup$
          @Zoe I have edited the answer. It does hold even when LHS is $infty$ and sigma finiteness is required for the argument.
          $endgroup$
          – Kavi Rama Murthy
          Mar 24 at 5:30












          $begingroup$
          Thinks, now I think I can finish proof for the the case p=1
          $endgroup$
          – Zoe
          Mar 24 at 5:34




          $begingroup$
          Thinks, now I think I can finish proof for the the case p=1
          $endgroup$
          – Zoe
          Mar 24 at 5:34

















          draft saved

          draft discarded
















































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