Rate of convergence of the product of two random variable sequences

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Given that
$$forall epsilon_1 exists delta_epsilon_1>0, N_epsilon_1>0,text s.t. Pr n^alpha <epsilon_1 forall n>N_epsilon_1$$
$$forall epsilon_2 exists delta_epsilon_2>0, N_epsilon_2>0,text s.t. Pr n^beta <epsilon_2 forall n>N_epsilon_2 $$



How to prove that
$$forall epsilon exists delta_epsilon>0, N_epsilon>0,text s.t. Pr n^alpha+beta <epsilon forall n>N_epsilon $$



In other word, can we get $X_nY_n=O_p(n^-(alpha+beta))$ based on $X_n=O_p(n^-alpha)$ and $Y_n=O_p(n^-beta)$? what conditions should be added? Thanks!







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  • 1




    Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
    – Michael
    Jul 23 at 23:56











  • Yes, I will correct it, thanks!
    – Carlton Chen
    Jul 23 at 23:59






  • 1




    What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
    – Michael
    Jul 24 at 0:00











  • You didn't actually correct it; it still says $X_n$ in the second inequality.
    – joriki
    Jul 24 at 3:30










  • Thank you @Michael, I guess the complete proof shoyld be:
    – Carlton Chen
    Jul 24 at 13:52














up vote
1
down vote

favorite
1












Given that
$$forall epsilon_1 exists delta_epsilon_1>0, N_epsilon_1>0,text s.t. Pr n^alpha <epsilon_1 forall n>N_epsilon_1$$
$$forall epsilon_2 exists delta_epsilon_2>0, N_epsilon_2>0,text s.t. Pr n^beta <epsilon_2 forall n>N_epsilon_2 $$



How to prove that
$$forall epsilon exists delta_epsilon>0, N_epsilon>0,text s.t. Pr n^alpha+beta <epsilon forall n>N_epsilon $$



In other word, can we get $X_nY_n=O_p(n^-(alpha+beta))$ based on $X_n=O_p(n^-alpha)$ and $Y_n=O_p(n^-beta)$? what conditions should be added? Thanks!







share|cite|improve this question

















  • 1




    Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
    – Michael
    Jul 23 at 23:56











  • Yes, I will correct it, thanks!
    – Carlton Chen
    Jul 23 at 23:59






  • 1




    What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
    – Michael
    Jul 24 at 0:00











  • You didn't actually correct it; it still says $X_n$ in the second inequality.
    – joriki
    Jul 24 at 3:30










  • Thank you @Michael, I guess the complete proof shoyld be:
    – Carlton Chen
    Jul 24 at 13:52












up vote
1
down vote

favorite
1









up vote
1
down vote

favorite
1






1





Given that
$$forall epsilon_1 exists delta_epsilon_1>0, N_epsilon_1>0,text s.t. Pr n^alpha <epsilon_1 forall n>N_epsilon_1$$
$$forall epsilon_2 exists delta_epsilon_2>0, N_epsilon_2>0,text s.t. Pr n^beta <epsilon_2 forall n>N_epsilon_2 $$



How to prove that
$$forall epsilon exists delta_epsilon>0, N_epsilon>0,text s.t. Pr n^alpha+beta <epsilon forall n>N_epsilon $$



In other word, can we get $X_nY_n=O_p(n^-(alpha+beta))$ based on $X_n=O_p(n^-alpha)$ and $Y_n=O_p(n^-beta)$? what conditions should be added? Thanks!







share|cite|improve this question













Given that
$$forall epsilon_1 exists delta_epsilon_1>0, N_epsilon_1>0,text s.t. Pr n^alpha <epsilon_1 forall n>N_epsilon_1$$
$$forall epsilon_2 exists delta_epsilon_2>0, N_epsilon_2>0,text s.t. Pr n^beta <epsilon_2 forall n>N_epsilon_2 $$



How to prove that
$$forall epsilon exists delta_epsilon>0, N_epsilon>0,text s.t. Pr n^alpha+beta <epsilon forall n>N_epsilon $$



In other word, can we get $X_nY_n=O_p(n^-(alpha+beta))$ based on $X_n=O_p(n^-alpha)$ and $Y_n=O_p(n^-beta)$? what conditions should be added? Thanks!









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Jul 24 at 9:55
























asked Jul 23 at 23:54









Carlton Chen

62




62







  • 1




    Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
    – Michael
    Jul 23 at 23:56











  • Yes, I will correct it, thanks!
    – Carlton Chen
    Jul 23 at 23:59






  • 1




    What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
    – Michael
    Jul 24 at 0:00











  • You didn't actually correct it; it still says $X_n$ in the second inequality.
    – joriki
    Jul 24 at 3:30










  • Thank you @Michael, I guess the complete proof shoyld be:
    – Carlton Chen
    Jul 24 at 13:52












  • 1




    Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
    – Michael
    Jul 23 at 23:56











  • Yes, I will correct it, thanks!
    – Carlton Chen
    Jul 23 at 23:59






  • 1




    What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
    – Michael
    Jul 24 at 0:00











  • You didn't actually correct it; it still says $X_n$ in the second inequality.
    – joriki
    Jul 24 at 3:30










  • Thank you @Michael, I guess the complete proof shoyld be:
    – Carlton Chen
    Jul 24 at 13:52







1




1




Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
– Michael
Jul 23 at 23:56





Likely the second inequality should have $epsilon_2$ inside the $Pr$. Also, should that have $Y_n$ instead of $X_n$? Else, $Y_n$ is not introduced anywhere.
– Michael
Jul 23 at 23:56













Yes, I will correct it, thanks!
– Carlton Chen
Jul 23 at 23:59




Yes, I will correct it, thanks!
– Carlton Chen
Jul 23 at 23:59




1




1




What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
– Michael
Jul 24 at 0:00





What if you use the following (assuming $delta>0$): $$>deltasubseteq >sqrtdelta cup $$
– Michael
Jul 24 at 0:00













You didn't actually correct it; it still says $X_n$ in the second inequality.
– joriki
Jul 24 at 3:30




You didn't actually correct it; it still says $X_n$ in the second inequality.
– joriki
Jul 24 at 3:30












Thank you @Michael, I guess the complete proof shoyld be:
– Carlton Chen
Jul 24 at 13:52




Thank you @Michael, I guess the complete proof shoyld be:
– Carlton Chen
Jul 24 at 13:52










1 Answer
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Thank you @Michael. I guess the proof shuold be: $forall epsilon_1<fracepsilon2, epsilon_2<fracepsilon2, exists delta_1gedelta_epsilon_1gesqrtdelta, delta_2gedelta_epsilon_2gesqrtdelta,
N_epsilon_1,delta_1ge 0, N_epsilon_2,delta_2ge 0$ s.t.



beginalign*
P n^alpha+beta &le P ge delta_1 + P n^beta \
&le fracepsilon2 + fracepsilon2 \
&= epsilon textfor forall n>maxN_epsilon_1,delta_1, N_epsilon_2,delta_2
endalign*



Am I right?






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    up vote
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    down vote













    Thank you @Michael. I guess the proof shuold be: $forall epsilon_1<fracepsilon2, epsilon_2<fracepsilon2, exists delta_1gedelta_epsilon_1gesqrtdelta, delta_2gedelta_epsilon_2gesqrtdelta,
    N_epsilon_1,delta_1ge 0, N_epsilon_2,delta_2ge 0$ s.t.



    beginalign*
    P n^alpha+beta &le P ge delta_1 + P n^beta \
    &le fracepsilon2 + fracepsilon2 \
    &= epsilon textfor forall n>maxN_epsilon_1,delta_1, N_epsilon_2,delta_2
    endalign*



    Am I right?






    share|cite|improve this answer

























      up vote
      0
      down vote













      Thank you @Michael. I guess the proof shuold be: $forall epsilon_1<fracepsilon2, epsilon_2<fracepsilon2, exists delta_1gedelta_epsilon_1gesqrtdelta, delta_2gedelta_epsilon_2gesqrtdelta,
      N_epsilon_1,delta_1ge 0, N_epsilon_2,delta_2ge 0$ s.t.



      beginalign*
      P n^alpha+beta &le P ge delta_1 + P n^beta \
      &le fracepsilon2 + fracepsilon2 \
      &= epsilon textfor forall n>maxN_epsilon_1,delta_1, N_epsilon_2,delta_2
      endalign*



      Am I right?






      share|cite|improve this answer























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        0
        down vote










        up vote
        0
        down vote









        Thank you @Michael. I guess the proof shuold be: $forall epsilon_1<fracepsilon2, epsilon_2<fracepsilon2, exists delta_1gedelta_epsilon_1gesqrtdelta, delta_2gedelta_epsilon_2gesqrtdelta,
        N_epsilon_1,delta_1ge 0, N_epsilon_2,delta_2ge 0$ s.t.



        beginalign*
        P n^alpha+beta &le P ge delta_1 + P n^beta \
        &le fracepsilon2 + fracepsilon2 \
        &= epsilon textfor forall n>maxN_epsilon_1,delta_1, N_epsilon_2,delta_2
        endalign*



        Am I right?






        share|cite|improve this answer













        Thank you @Michael. I guess the proof shuold be: $forall epsilon_1<fracepsilon2, epsilon_2<fracepsilon2, exists delta_1gedelta_epsilon_1gesqrtdelta, delta_2gedelta_epsilon_2gesqrtdelta,
        N_epsilon_1,delta_1ge 0, N_epsilon_2,delta_2ge 0$ s.t.



        beginalign*
        P n^alpha+beta &le P ge delta_1 + P n^beta \
        &le fracepsilon2 + fracepsilon2 \
        &= epsilon textfor forall n>maxN_epsilon_1,delta_1, N_epsilon_2,delta_2
        endalign*



        Am I right?







        share|cite|improve this answer













        share|cite|improve this answer



        share|cite|improve this answer











        answered Jul 24 at 13:54









        Carlton Chen

        62




        62






















             

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