Construction of a (jointly?) stationary and ergodic vector sequence.












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In a recent effort to understand stationary ergodic processes, I stumbled upon a paper that leaves me somewhat puzzled. I would be very grateful for any pointers.



The line of reasoning is as follows:



Given a set of assumptions, it is deduced that a random sequence ${f_t:tinmathbb{Z}}$ is stationary ergodic.
For any measurable map $h$, stationary ergodicity of ${f_t:tinmathbb{Z}}$ implies that ${h(f_t):tinmathbb{Z}}$ is stationary ergodic.



Moreover, there is a sequence of innovations ${u_t:tinmathbb{Z}}$ - also presumed stationary ergodic.



Given these facts, the paper goes on to assert (verbatim)




Together with ${u_t}$ being SE (Assumption 3), it follows that
${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence.




The proof concludes with the insight that: Continuity, and thus by extension, measurability of another function $g,:,mathbb{R}^2tomathbb{R}$ in turn implies that ${g(u_t,h(f_t))}$ is stationary ergodic.



At this point my struggle is with the statement that “${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence”.
While it was shown that ${u_t}$ and ${f_t}$ are stationary ergodic, I do not see how that necessarily implies that
${(u_t,h(f_t))}$ is jointly stationary ergodic. However, I am under the impression that this is a requirement for ${g(u_t,h(f_t))}$ to be stationary ergodic.



I would very much appreciate if anyone could tell me where I am going wrong, or wether I am missing any crucial piece of information - such as ${u_t}$ is assumed to be iid (?).



Thank you so very much.



Best,

Jon










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$endgroup$

















    1












    $begingroup$


    In a recent effort to understand stationary ergodic processes, I stumbled upon a paper that leaves me somewhat puzzled. I would be very grateful for any pointers.



    The line of reasoning is as follows:



    Given a set of assumptions, it is deduced that a random sequence ${f_t:tinmathbb{Z}}$ is stationary ergodic.
    For any measurable map $h$, stationary ergodicity of ${f_t:tinmathbb{Z}}$ implies that ${h(f_t):tinmathbb{Z}}$ is stationary ergodic.



    Moreover, there is a sequence of innovations ${u_t:tinmathbb{Z}}$ - also presumed stationary ergodic.



    Given these facts, the paper goes on to assert (verbatim)




    Together with ${u_t}$ being SE (Assumption 3), it follows that
    ${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence.




    The proof concludes with the insight that: Continuity, and thus by extension, measurability of another function $g,:,mathbb{R}^2tomathbb{R}$ in turn implies that ${g(u_t,h(f_t))}$ is stationary ergodic.



    At this point my struggle is with the statement that “${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence”.
    While it was shown that ${u_t}$ and ${f_t}$ are stationary ergodic, I do not see how that necessarily implies that
    ${(u_t,h(f_t))}$ is jointly stationary ergodic. However, I am under the impression that this is a requirement for ${g(u_t,h(f_t))}$ to be stationary ergodic.



    I would very much appreciate if anyone could tell me where I am going wrong, or wether I am missing any crucial piece of information - such as ${u_t}$ is assumed to be iid (?).



    Thank you so very much.



    Best,

    Jon










    share|cite|improve this question









    $endgroup$















      1












      1








      1





      $begingroup$


      In a recent effort to understand stationary ergodic processes, I stumbled upon a paper that leaves me somewhat puzzled. I would be very grateful for any pointers.



      The line of reasoning is as follows:



      Given a set of assumptions, it is deduced that a random sequence ${f_t:tinmathbb{Z}}$ is stationary ergodic.
      For any measurable map $h$, stationary ergodicity of ${f_t:tinmathbb{Z}}$ implies that ${h(f_t):tinmathbb{Z}}$ is stationary ergodic.



      Moreover, there is a sequence of innovations ${u_t:tinmathbb{Z}}$ - also presumed stationary ergodic.



      Given these facts, the paper goes on to assert (verbatim)




      Together with ${u_t}$ being SE (Assumption 3), it follows that
      ${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence.




      The proof concludes with the insight that: Continuity, and thus by extension, measurability of another function $g,:,mathbb{R}^2tomathbb{R}$ in turn implies that ${g(u_t,h(f_t))}$ is stationary ergodic.



      At this point my struggle is with the statement that “${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence”.
      While it was shown that ${u_t}$ and ${f_t}$ are stationary ergodic, I do not see how that necessarily implies that
      ${(u_t,h(f_t))}$ is jointly stationary ergodic. However, I am under the impression that this is a requirement for ${g(u_t,h(f_t))}$ to be stationary ergodic.



      I would very much appreciate if anyone could tell me where I am going wrong, or wether I am missing any crucial piece of information - such as ${u_t}$ is assumed to be iid (?).



      Thank you so very much.



      Best,

      Jon










      share|cite|improve this question









      $endgroup$




      In a recent effort to understand stationary ergodic processes, I stumbled upon a paper that leaves me somewhat puzzled. I would be very grateful for any pointers.



      The line of reasoning is as follows:



      Given a set of assumptions, it is deduced that a random sequence ${f_t:tinmathbb{Z}}$ is stationary ergodic.
      For any measurable map $h$, stationary ergodicity of ${f_t:tinmathbb{Z}}$ implies that ${h(f_t):tinmathbb{Z}}$ is stationary ergodic.



      Moreover, there is a sequence of innovations ${u_t:tinmathbb{Z}}$ - also presumed stationary ergodic.



      Given these facts, the paper goes on to assert (verbatim)




      Together with ${u_t}$ being SE (Assumption 3), it follows that
      ${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence.




      The proof concludes with the insight that: Continuity, and thus by extension, measurability of another function $g,:,mathbb{R}^2tomathbb{R}$ in turn implies that ${g(u_t,h(f_t))}$ is stationary ergodic.



      At this point my struggle is with the statement that “${(u_t,h(f_t))}$ is a stationary and ergodic vector sequence”.
      While it was shown that ${u_t}$ and ${f_t}$ are stationary ergodic, I do not see how that necessarily implies that
      ${(u_t,h(f_t))}$ is jointly stationary ergodic. However, I am under the impression that this is a requirement for ${g(u_t,h(f_t))}$ to be stationary ergodic.



      I would very much appreciate if anyone could tell me where I am going wrong, or wether I am missing any crucial piece of information - such as ${u_t}$ is assumed to be iid (?).



      Thank you so very much.



      Best,

      Jon







      real-analysis probability-theory measure-theory stochastic-processes ergodic-theory






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      asked Jan 3 at 16:53









      J.BeckJ.Beck

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