Stationary distribution of DTMC with infinite state space

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I am solving the stationary distirbution of a Discrete time Markov Chain with infinite state space. The state space is $pi^H_0,pi^H_1,...,pi^L_0,pi^L_1,...$. The transition matrix has structure. I eventually reduce the system linear equations into the following two series. But feel no clue about how to start to solve them....
beginalign*
&begincases
&pi^H_0=api^H_1\
&pi^H_1=api^H_0+api^H_2+cpi^L_0\
&pi^H_n=bpi^H_n-1+api^H_n+1,~forall~ngeq 2
endcases~~
begincases
&pi^L_0=cpi^L_1\
&pi^L_1=bpi^H_0+dpi^L_0+cpi^L_2\
&pi^L_n=dpi^L_n-1+cpi^L_n+1,~forall~ngeq 2
endcases\
&sum_n=0^infty(pi^H_n+pi^L_n)=1\
&a+b=1,~c+d=1,~a,b,c,d~mboxare all positive constant pi^H_n_n=0^infty~mboxand pi^L_n_n=0^infty~mboxare all non-negative variables
endalign*










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  • "The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
    – Did
    Sep 9 at 9:41










  • @Did Yes, sorry for my bad notation
    – KevinKim
    Sep 9 at 10:12














up vote
0
down vote

favorite












I am solving the stationary distirbution of a Discrete time Markov Chain with infinite state space. The state space is $pi^H_0,pi^H_1,...,pi^L_0,pi^L_1,...$. The transition matrix has structure. I eventually reduce the system linear equations into the following two series. But feel no clue about how to start to solve them....
beginalign*
&begincases
&pi^H_0=api^H_1\
&pi^H_1=api^H_0+api^H_2+cpi^L_0\
&pi^H_n=bpi^H_n-1+api^H_n+1,~forall~ngeq 2
endcases~~
begincases
&pi^L_0=cpi^L_1\
&pi^L_1=bpi^H_0+dpi^L_0+cpi^L_2\
&pi^L_n=dpi^L_n-1+cpi^L_n+1,~forall~ngeq 2
endcases\
&sum_n=0^infty(pi^H_n+pi^L_n)=1\
&a+b=1,~c+d=1,~a,b,c,d~mboxare all positive constant pi^H_n_n=0^infty~mboxand pi^L_n_n=0^infty~mboxare all non-negative variables
endalign*










share|cite|improve this question





















  • "The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
    – Did
    Sep 9 at 9:41










  • @Did Yes, sorry for my bad notation
    – KevinKim
    Sep 9 at 10:12












up vote
0
down vote

favorite









up vote
0
down vote

favorite











I am solving the stationary distirbution of a Discrete time Markov Chain with infinite state space. The state space is $pi^H_0,pi^H_1,...,pi^L_0,pi^L_1,...$. The transition matrix has structure. I eventually reduce the system linear equations into the following two series. But feel no clue about how to start to solve them....
beginalign*
&begincases
&pi^H_0=api^H_1\
&pi^H_1=api^H_0+api^H_2+cpi^L_0\
&pi^H_n=bpi^H_n-1+api^H_n+1,~forall~ngeq 2
endcases~~
begincases
&pi^L_0=cpi^L_1\
&pi^L_1=bpi^H_0+dpi^L_0+cpi^L_2\
&pi^L_n=dpi^L_n-1+cpi^L_n+1,~forall~ngeq 2
endcases\
&sum_n=0^infty(pi^H_n+pi^L_n)=1\
&a+b=1,~c+d=1,~a,b,c,d~mboxare all positive constant pi^H_n_n=0^infty~mboxand pi^L_n_n=0^infty~mboxare all non-negative variables
endalign*










share|cite|improve this question













I am solving the stationary distirbution of a Discrete time Markov Chain with infinite state space. The state space is $pi^H_0,pi^H_1,...,pi^L_0,pi^L_1,...$. The transition matrix has structure. I eventually reduce the system linear equations into the following two series. But feel no clue about how to start to solve them....
beginalign*
&begincases
&pi^H_0=api^H_1\
&pi^H_1=api^H_0+api^H_2+cpi^L_0\
&pi^H_n=bpi^H_n-1+api^H_n+1,~forall~ngeq 2
endcases~~
begincases
&pi^L_0=cpi^L_1\
&pi^L_1=bpi^H_0+dpi^L_0+cpi^L_2\
&pi^L_n=dpi^L_n-1+cpi^L_n+1,~forall~ngeq 2
endcases\
&sum_n=0^infty(pi^H_n+pi^L_n)=1\
&a+b=1,~c+d=1,~a,b,c,d~mboxare all positive constant pi^H_n_n=0^infty~mboxand pi^L_n_n=0^infty~mboxare all non-negative variables
endalign*







markov-chains markov-process






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asked Sep 9 at 8:30









KevinKim

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  • "The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
    – Did
    Sep 9 at 9:41










  • @Did Yes, sorry for my bad notation
    – KevinKim
    Sep 9 at 10:12
















  • "The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
    – Did
    Sep 9 at 9:41










  • @Did Yes, sorry for my bad notation
    – KevinKim
    Sep 9 at 10:12















"The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
– Did
Sep 9 at 9:41




"The state space is $pi^H_0,pi^H_1,... ,pi^L_0,pi^L_1, ...$." You might mean that the state space is $$H,Ltimes0,1,2,ldots$$
– Did
Sep 9 at 9:41












@Did Yes, sorry for my bad notation
– KevinKim
Sep 9 at 10:12




@Did Yes, sorry for my bad notation
– KevinKim
Sep 9 at 10:12










1 Answer
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The recurrences in the third lines aren't coupled, so they can be solved with the standard ansatz $pi_k^H=lambda^k$:



$$
lambda^n=blambda^n-1+alambda^n+1;,
$$



which yields the characteristic equation



$$
alambda^2-lambda+b=0
$$



(and likewise for $pi^L$). This yields two linearly independent solutions each, for a total of $4$ free coefficients. The first two lines allow you to express the values for $n=1,2$ in terms of the initial values for $n=0$, yielding one condition each. That leaves two degrees of freedom, and normalization reduces this to one. This might be eliminated if one of the characteristic values has magnitude greater than $1$ and thus isn't suitable for representing probabilities.






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    1 Answer
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    1 Answer
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    active

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    up vote
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    down vote













    The recurrences in the third lines aren't coupled, so they can be solved with the standard ansatz $pi_k^H=lambda^k$:



    $$
    lambda^n=blambda^n-1+alambda^n+1;,
    $$



    which yields the characteristic equation



    $$
    alambda^2-lambda+b=0
    $$



    (and likewise for $pi^L$). This yields two linearly independent solutions each, for a total of $4$ free coefficients. The first two lines allow you to express the values for $n=1,2$ in terms of the initial values for $n=0$, yielding one condition each. That leaves two degrees of freedom, and normalization reduces this to one. This might be eliminated if one of the characteristic values has magnitude greater than $1$ and thus isn't suitable for representing probabilities.






    share|cite|improve this answer
























      up vote
      1
      down vote













      The recurrences in the third lines aren't coupled, so they can be solved with the standard ansatz $pi_k^H=lambda^k$:



      $$
      lambda^n=blambda^n-1+alambda^n+1;,
      $$



      which yields the characteristic equation



      $$
      alambda^2-lambda+b=0
      $$



      (and likewise for $pi^L$). This yields two linearly independent solutions each, for a total of $4$ free coefficients. The first two lines allow you to express the values for $n=1,2$ in terms of the initial values for $n=0$, yielding one condition each. That leaves two degrees of freedom, and normalization reduces this to one. This might be eliminated if one of the characteristic values has magnitude greater than $1$ and thus isn't suitable for representing probabilities.






      share|cite|improve this answer






















        up vote
        1
        down vote










        up vote
        1
        down vote









        The recurrences in the third lines aren't coupled, so they can be solved with the standard ansatz $pi_k^H=lambda^k$:



        $$
        lambda^n=blambda^n-1+alambda^n+1;,
        $$



        which yields the characteristic equation



        $$
        alambda^2-lambda+b=0
        $$



        (and likewise for $pi^L$). This yields two linearly independent solutions each, for a total of $4$ free coefficients. The first two lines allow you to express the values for $n=1,2$ in terms of the initial values for $n=0$, yielding one condition each. That leaves two degrees of freedom, and normalization reduces this to one. This might be eliminated if one of the characteristic values has magnitude greater than $1$ and thus isn't suitable for representing probabilities.






        share|cite|improve this answer












        The recurrences in the third lines aren't coupled, so they can be solved with the standard ansatz $pi_k^H=lambda^k$:



        $$
        lambda^n=blambda^n-1+alambda^n+1;,
        $$



        which yields the characteristic equation



        $$
        alambda^2-lambda+b=0
        $$



        (and likewise for $pi^L$). This yields two linearly independent solutions each, for a total of $4$ free coefficients. The first two lines allow you to express the values for $n=1,2$ in terms of the initial values for $n=0$, yielding one condition each. That leaves two degrees of freedom, and normalization reduces this to one. This might be eliminated if one of the characteristic values has magnitude greater than $1$ and thus isn't suitable for representing probabilities.







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        answered Sep 9 at 8:55









        joriki

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