Chapman-Kolmogorov equations, continuous time Markov chains, why do they have this solution.

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$P^'(t)=QP(t)=P(t)Q$



These are the Chapman-Kolmogorov backward and forward equations for a countable sate space continuous time Markov Chain. They have the solution,



$
P(t)=e^Qt
$



I have two questions



1) in the finite state space case, why is this a solution?



2) In the case where we have an infinite state space and the above are the infinite matrices how do we get this as a solution? I know this is a much harder question so maybe just a brief outline of an answer will help. Does the problem come from bringing the derivative inside the infinite sum?







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    up vote
    0
    down vote

    favorite












    $P^'(t)=QP(t)=P(t)Q$



    These are the Chapman-Kolmogorov backward and forward equations for a countable sate space continuous time Markov Chain. They have the solution,



    $
    P(t)=e^Qt
    $



    I have two questions



    1) in the finite state space case, why is this a solution?



    2) In the case where we have an infinite state space and the above are the infinite matrices how do we get this as a solution? I know this is a much harder question so maybe just a brief outline of an answer will help. Does the problem come from bringing the derivative inside the infinite sum?







    share|cite|improve this question























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      $P^'(t)=QP(t)=P(t)Q$



      These are the Chapman-Kolmogorov backward and forward equations for a countable sate space continuous time Markov Chain. They have the solution,



      $
      P(t)=e^Qt
      $



      I have two questions



      1) in the finite state space case, why is this a solution?



      2) In the case where we have an infinite state space and the above are the infinite matrices how do we get this as a solution? I know this is a much harder question so maybe just a brief outline of an answer will help. Does the problem come from bringing the derivative inside the infinite sum?







      share|cite|improve this question













      $P^'(t)=QP(t)=P(t)Q$



      These are the Chapman-Kolmogorov backward and forward equations for a countable sate space continuous time Markov Chain. They have the solution,



      $
      P(t)=e^Qt
      $



      I have two questions



      1) in the finite state space case, why is this a solution?



      2) In the case where we have an infinite state space and the above are the infinite matrices how do we get this as a solution? I know this is a much harder question so maybe just a brief outline of an answer will help. Does the problem come from bringing the derivative inside the infinite sum?









      share|cite|improve this question












      share|cite|improve this question




      share|cite|improve this question








      edited Aug 2 at 22:19
























      asked Aug 2 at 18:37









      Monty

      15212




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          1) This just the solution of this ODE. You can compute it using for instance the definition of the matrix exponential:
          $$e^A = sum_j=0^infty frac1j!A^j.$$
          We have $$P(t) = e^tQ = sum_j=0^infty frac1j!t^jQ^j.$$
          When differentiating $P(t)$ w.r.t. to $t$, you obtain $$P'(t) = sum_j=1^infty frac1j!(jt^j-1)Q^j = left(sum_j=1^infty frac1(j-1)!t^j-1Q^j-1right)Q = P(t)Q.$$
          Equivalently you can bracket the single $Q$ out to the left and obtain $P'(t) = QP(t)$.



          2) I think, when using the definition of the matrix exponential above, you can prove the same statement also for the infinite state space case.






          share|cite|improve this answer





















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            1) This just the solution of this ODE. You can compute it using for instance the definition of the matrix exponential:
            $$e^A = sum_j=0^infty frac1j!A^j.$$
            We have $$P(t) = e^tQ = sum_j=0^infty frac1j!t^jQ^j.$$
            When differentiating $P(t)$ w.r.t. to $t$, you obtain $$P'(t) = sum_j=1^infty frac1j!(jt^j-1)Q^j = left(sum_j=1^infty frac1(j-1)!t^j-1Q^j-1right)Q = P(t)Q.$$
            Equivalently you can bracket the single $Q$ out to the left and obtain $P'(t) = QP(t)$.



            2) I think, when using the definition of the matrix exponential above, you can prove the same statement also for the infinite state space case.






            share|cite|improve this answer

























              up vote
              0
              down vote













              1) This just the solution of this ODE. You can compute it using for instance the definition of the matrix exponential:
              $$e^A = sum_j=0^infty frac1j!A^j.$$
              We have $$P(t) = e^tQ = sum_j=0^infty frac1j!t^jQ^j.$$
              When differentiating $P(t)$ w.r.t. to $t$, you obtain $$P'(t) = sum_j=1^infty frac1j!(jt^j-1)Q^j = left(sum_j=1^infty frac1(j-1)!t^j-1Q^j-1right)Q = P(t)Q.$$
              Equivalently you can bracket the single $Q$ out to the left and obtain $P'(t) = QP(t)$.



              2) I think, when using the definition of the matrix exponential above, you can prove the same statement also for the infinite state space case.






              share|cite|improve this answer























                up vote
                0
                down vote










                up vote
                0
                down vote









                1) This just the solution of this ODE. You can compute it using for instance the definition of the matrix exponential:
                $$e^A = sum_j=0^infty frac1j!A^j.$$
                We have $$P(t) = e^tQ = sum_j=0^infty frac1j!t^jQ^j.$$
                When differentiating $P(t)$ w.r.t. to $t$, you obtain $$P'(t) = sum_j=1^infty frac1j!(jt^j-1)Q^j = left(sum_j=1^infty frac1(j-1)!t^j-1Q^j-1right)Q = P(t)Q.$$
                Equivalently you can bracket the single $Q$ out to the left and obtain $P'(t) = QP(t)$.



                2) I think, when using the definition of the matrix exponential above, you can prove the same statement also for the infinite state space case.






                share|cite|improve this answer













                1) This just the solution of this ODE. You can compute it using for instance the definition of the matrix exponential:
                $$e^A = sum_j=0^infty frac1j!A^j.$$
                We have $$P(t) = e^tQ = sum_j=0^infty frac1j!t^jQ^j.$$
                When differentiating $P(t)$ w.r.t. to $t$, you obtain $$P'(t) = sum_j=1^infty frac1j!(jt^j-1)Q^j = left(sum_j=1^infty frac1(j-1)!t^j-1Q^j-1right)Q = P(t)Q.$$
                Equivalently you can bracket the single $Q$ out to the left and obtain $P'(t) = QP(t)$.



                2) I think, when using the definition of the matrix exponential above, you can prove the same statement also for the infinite state space case.







                share|cite|improve this answer













                share|cite|improve this answer



                share|cite|improve this answer











                answered Aug 2 at 18:57









                Jonas

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