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Does a strong solution to a SDE imply lipschitz condition?


Growth condition for Ito diffusionsIs the solution to a driftless SDE with Lipschitz variation a martingale?existence/uniqueness of solution and Ito's formulaExample of a regular strong solution of an SDE, which doesn't satisfy a Lyapunov condition?Is the distribution of an Ito diffusion at time t absolutely continuous wrt Lebesgue measure?Strong solution SDE - independence of initial conditiionExistence and uniqueness of solution of a non linear SDEHow to prove a solution of SDE with Lipschitz condition is unbounded?Is the solution to this (simple) Stochastic Differential Equation unique?SDE existence and uniqueness













2












$begingroup$


Consider $dX_t=b(X_t,t)dt+sigma(X_t,t)dB_t$. I know that,



$|b(x,t)-b(y,t)|+|sigma(x,t)-sigma(y,t)|leq D|x-y|$ for some constant D implies the existence and uniqueness of a strong solution. However in Oksendal, to show that $dX_t=sign(X_t)dB_t$ doesn't have a strong solution another proof is presented, even though $sign(x)$ fails the lipschitz condition. I have seen it at a couple of more places for this equation.



My question: Is Lipschitz condition an iff condition for a strong solution?










share|cite|improve this question











$endgroup$
















    2












    $begingroup$


    Consider $dX_t=b(X_t,t)dt+sigma(X_t,t)dB_t$. I know that,



    $|b(x,t)-b(y,t)|+|sigma(x,t)-sigma(y,t)|leq D|x-y|$ for some constant D implies the existence and uniqueness of a strong solution. However in Oksendal, to show that $dX_t=sign(X_t)dB_t$ doesn't have a strong solution another proof is presented, even though $sign(x)$ fails the lipschitz condition. I have seen it at a couple of more places for this equation.



    My question: Is Lipschitz condition an iff condition for a strong solution?










    share|cite|improve this question











    $endgroup$














      2












      2








      2


      3



      $begingroup$


      Consider $dX_t=b(X_t,t)dt+sigma(X_t,t)dB_t$. I know that,



      $|b(x,t)-b(y,t)|+|sigma(x,t)-sigma(y,t)|leq D|x-y|$ for some constant D implies the existence and uniqueness of a strong solution. However in Oksendal, to show that $dX_t=sign(X_t)dB_t$ doesn't have a strong solution another proof is presented, even though $sign(x)$ fails the lipschitz condition. I have seen it at a couple of more places for this equation.



      My question: Is Lipschitz condition an iff condition for a strong solution?










      share|cite|improve this question











      $endgroup$




      Consider $dX_t=b(X_t,t)dt+sigma(X_t,t)dB_t$. I know that,



      $|b(x,t)-b(y,t)|+|sigma(x,t)-sigma(y,t)|leq D|x-y|$ for some constant D implies the existence and uniqueness of a strong solution. However in Oksendal, to show that $dX_t=sign(X_t)dB_t$ doesn't have a strong solution another proof is presented, even though $sign(x)$ fails the lipschitz condition. I have seen it at a couple of more places for this equation.



      My question: Is Lipschitz condition an iff condition for a strong solution?







      stochastic-calculus stochastic-integrals stochastic-analysis






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited 4 hours ago







      Who cares

















      asked 5 hours ago









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      16713




















          1 Answer
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          4












          $begingroup$

          No, Lipschitz continuity is not a necessary condition for the existence of a strong solution. There is, for instance, the following general result which goes back to Zvonkin:




          Let $(B_t)_t geq 0$ be a one-dimensional Bownian motion. If the coefficients of the SDE $$dX_t = b(t,X_t) , dt + sigma(t,X_t) , dB_t, qquad X_0 = x_0, tag1$$ are bounded, $b$ is measurable, $sigma$ is continuous and there exist constants $C>0$ and $epsilon>0$ such that $$|sigma(t,x)-sigma(t,y)| leq C sqrt quad textand quad |sigma(t,x)| geq epsilon$$ for all $t geq 0$, $x,y in mathbbR$, then the SDE $(1)$ has a (unique) strong solution.




          Note that the result does not require any regularity assumptions on the drift $b$ (except from measurability) and only Hölder continuity of order $1/2$ for the diffusion coefficient $sigma$.



          A nice overview on known existence and uniqueness results for SDEs can be found in the book Singular Stochastic Differential Equations by Cherny & Engelbert.






          share|cite|improve this answer









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            1 Answer
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            4












            $begingroup$

            No, Lipschitz continuity is not a necessary condition for the existence of a strong solution. There is, for instance, the following general result which goes back to Zvonkin:




            Let $(B_t)_t geq 0$ be a one-dimensional Bownian motion. If the coefficients of the SDE $$dX_t = b(t,X_t) , dt + sigma(t,X_t) , dB_t, qquad X_0 = x_0, tag1$$ are bounded, $b$ is measurable, $sigma$ is continuous and there exist constants $C>0$ and $epsilon>0$ such that $$|sigma(t,x)-sigma(t,y)| leq C sqrt quad textand quad |sigma(t,x)| geq epsilon$$ for all $t geq 0$, $x,y in mathbbR$, then the SDE $(1)$ has a (unique) strong solution.




            Note that the result does not require any regularity assumptions on the drift $b$ (except from measurability) and only Hölder continuity of order $1/2$ for the diffusion coefficient $sigma$.



            A nice overview on known existence and uniqueness results for SDEs can be found in the book Singular Stochastic Differential Equations by Cherny & Engelbert.






            share|cite|improve this answer









            $endgroup$

















              4












              $begingroup$

              No, Lipschitz continuity is not a necessary condition for the existence of a strong solution. There is, for instance, the following general result which goes back to Zvonkin:




              Let $(B_t)_t geq 0$ be a one-dimensional Bownian motion. If the coefficients of the SDE $$dX_t = b(t,X_t) , dt + sigma(t,X_t) , dB_t, qquad X_0 = x_0, tag1$$ are bounded, $b$ is measurable, $sigma$ is continuous and there exist constants $C>0$ and $epsilon>0$ such that $$|sigma(t,x)-sigma(t,y)| leq C sqrt quad textand quad |sigma(t,x)| geq epsilon$$ for all $t geq 0$, $x,y in mathbbR$, then the SDE $(1)$ has a (unique) strong solution.




              Note that the result does not require any regularity assumptions on the drift $b$ (except from measurability) and only Hölder continuity of order $1/2$ for the diffusion coefficient $sigma$.



              A nice overview on known existence and uniqueness results for SDEs can be found in the book Singular Stochastic Differential Equations by Cherny & Engelbert.






              share|cite|improve this answer









              $endgroup$















                4












                4








                4





                $begingroup$

                No, Lipschitz continuity is not a necessary condition for the existence of a strong solution. There is, for instance, the following general result which goes back to Zvonkin:




                Let $(B_t)_t geq 0$ be a one-dimensional Bownian motion. If the coefficients of the SDE $$dX_t = b(t,X_t) , dt + sigma(t,X_t) , dB_t, qquad X_0 = x_0, tag1$$ are bounded, $b$ is measurable, $sigma$ is continuous and there exist constants $C>0$ and $epsilon>0$ such that $$|sigma(t,x)-sigma(t,y)| leq C sqrt quad textand quad |sigma(t,x)| geq epsilon$$ for all $t geq 0$, $x,y in mathbbR$, then the SDE $(1)$ has a (unique) strong solution.




                Note that the result does not require any regularity assumptions on the drift $b$ (except from measurability) and only Hölder continuity of order $1/2$ for the diffusion coefficient $sigma$.



                A nice overview on known existence and uniqueness results for SDEs can be found in the book Singular Stochastic Differential Equations by Cherny & Engelbert.






                share|cite|improve this answer









                $endgroup$



                No, Lipschitz continuity is not a necessary condition for the existence of a strong solution. There is, for instance, the following general result which goes back to Zvonkin:




                Let $(B_t)_t geq 0$ be a one-dimensional Bownian motion. If the coefficients of the SDE $$dX_t = b(t,X_t) , dt + sigma(t,X_t) , dB_t, qquad X_0 = x_0, tag1$$ are bounded, $b$ is measurable, $sigma$ is continuous and there exist constants $C>0$ and $epsilon>0$ such that $$|sigma(t,x)-sigma(t,y)| leq C sqrt quad textand quad |sigma(t,x)| geq epsilon$$ for all $t geq 0$, $x,y in mathbbR$, then the SDE $(1)$ has a (unique) strong solution.




                Note that the result does not require any regularity assumptions on the drift $b$ (except from measurability) and only Hölder continuity of order $1/2$ for the diffusion coefficient $sigma$.



                A nice overview on known existence and uniqueness results for SDEs can be found in the book Singular Stochastic Differential Equations by Cherny & Engelbert.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 3 hours ago









                sazsaz

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