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Filtering Sum of Brownian Motions



The 2019 Stack Overflow Developer Survey Results Are Ind-dimensional Brownian motion and martingalesLaws and Moments of two dimensional brownian motionsAbsorbed brownian motion is a Markov processFrom brownian bridge to brownian motion proofBrownian motions under different filtrations, quadratic covariation, covergence of approximating sumIs there a way to construct Brownian motion from a given Brownian motion?How to prove differential of product correlated Brownian Motions?Brownian motion in random landscapeCan we re-write the natural filtration of a Brownian Motion?Noisy Brownian Noise










0












$begingroup$


Let us assume that there exist two independent Brownian Motions $B_t$ and $W_t$, and consider their sum $Y_t=B_t + W_t$. Next, define the filtration generated by the sum, $mathcalF_t^Y=sigma(Y_u)_0
leq u leq t$
.



How would one compute the filter $E[ B_t | mathcalF_t^Y]$?



My intuition tells me that the solution to this filtering problem should just be $E[B_t | mathcalF_t^Y] = frac12 Y_t$, although I cannot prove it. As a secondary question, can we generalize to having independent continuous martingales instead of two Brownian Motions?



Any help is appreciated!










share|cite|improve this question











$endgroup$
















    0












    $begingroup$


    Let us assume that there exist two independent Brownian Motions $B_t$ and $W_t$, and consider their sum $Y_t=B_t + W_t$. Next, define the filtration generated by the sum, $mathcalF_t^Y=sigma(Y_u)_0
    leq u leq t$
    .



    How would one compute the filter $E[ B_t | mathcalF_t^Y]$?



    My intuition tells me that the solution to this filtering problem should just be $E[B_t | mathcalF_t^Y] = frac12 Y_t$, although I cannot prove it. As a secondary question, can we generalize to having independent continuous martingales instead of two Brownian Motions?



    Any help is appreciated!










    share|cite|improve this question











    $endgroup$














      0












      0








      0





      $begingroup$


      Let us assume that there exist two independent Brownian Motions $B_t$ and $W_t$, and consider their sum $Y_t=B_t + W_t$. Next, define the filtration generated by the sum, $mathcalF_t^Y=sigma(Y_u)_0
      leq u leq t$
      .



      How would one compute the filter $E[ B_t | mathcalF_t^Y]$?



      My intuition tells me that the solution to this filtering problem should just be $E[B_t | mathcalF_t^Y] = frac12 Y_t$, although I cannot prove it. As a secondary question, can we generalize to having independent continuous martingales instead of two Brownian Motions?



      Any help is appreciated!










      share|cite|improve this question











      $endgroup$




      Let us assume that there exist two independent Brownian Motions $B_t$ and $W_t$, and consider their sum $Y_t=B_t + W_t$. Next, define the filtration generated by the sum, $mathcalF_t^Y=sigma(Y_u)_0
      leq u leq t$
      .



      How would one compute the filter $E[ B_t | mathcalF_t^Y]$?



      My intuition tells me that the solution to this filtering problem should just be $E[B_t | mathcalF_t^Y] = frac12 Y_t$, although I cannot prove it. As a secondary question, can we generalize to having independent continuous martingales instead of two Brownian Motions?



      Any help is appreciated!







      stochastic-processes stochastic-calculus brownian-motion






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited 19 hours ago









      Henno Brandsma

      116k349127




      116k349127










      asked Apr 8 at 0:51









      Hotdog2000Hotdog2000

      678




      678




















          1 Answer
          1






          active

          oldest

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          0












          $begingroup$

          Looks like I solved this one already, so I will share the solution.
          $$
          Y_t = E[Y_t | mathcalF_t^Y] = E[B_t | mathcalF_t^Y] + E[W_t | mathcalF_t^Y]
          $$

          since $B_t$ and $W_t$ are identically distributed, we should have
          $$
          E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]
          $$

          and so we get that $frac12 Y_t = E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]$.






          share|cite|improve this answer









          $endgroup$













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            0












            $begingroup$

            Looks like I solved this one already, so I will share the solution.
            $$
            Y_t = E[Y_t | mathcalF_t^Y] = E[B_t | mathcalF_t^Y] + E[W_t | mathcalF_t^Y]
            $$

            since $B_t$ and $W_t$ are identically distributed, we should have
            $$
            E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]
            $$

            and so we get that $frac12 Y_t = E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]$.






            share|cite|improve this answer









            $endgroup$

















              0












              $begingroup$

              Looks like I solved this one already, so I will share the solution.
              $$
              Y_t = E[Y_t | mathcalF_t^Y] = E[B_t | mathcalF_t^Y] + E[W_t | mathcalF_t^Y]
              $$

              since $B_t$ and $W_t$ are identically distributed, we should have
              $$
              E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]
              $$

              and so we get that $frac12 Y_t = E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]$.






              share|cite|improve this answer









              $endgroup$















                0












                0








                0





                $begingroup$

                Looks like I solved this one already, so I will share the solution.
                $$
                Y_t = E[Y_t | mathcalF_t^Y] = E[B_t | mathcalF_t^Y] + E[W_t | mathcalF_t^Y]
                $$

                since $B_t$ and $W_t$ are identically distributed, we should have
                $$
                E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]
                $$

                and so we get that $frac12 Y_t = E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]$.






                share|cite|improve this answer









                $endgroup$



                Looks like I solved this one already, so I will share the solution.
                $$
                Y_t = E[Y_t | mathcalF_t^Y] = E[B_t | mathcalF_t^Y] + E[W_t | mathcalF_t^Y]
                $$

                since $B_t$ and $W_t$ are identically distributed, we should have
                $$
                E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]
                $$

                and so we get that $frac12 Y_t = E[B_t | mathcalF_t^Y] = E[W_t | mathcalF_t^Y]$.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered Apr 8 at 1:04









                Hotdog2000Hotdog2000

                678




                678



























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