Does $limlimits_{mrightarrowinfty}sumlimits_{k=m}^infty d(a_k,a_{k+1})$ equal to zero for any sequence...












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Let $(M,d)$ be a metric space and $(a_n)subset M$ a sequence. Is it always true that if $r_m=sumlimits_{k=m}^infty d(a_k,a_{k+1})$ we have $limlimits_{mrightarrowinfty}r_m=0$?



$$r_m=sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{m-1}d(a_k,a_{k+1})xrightarrow[mrightarrowinfty]{}sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{infty}d(a_k,a_{k+1})=0$$



Is this always correct or does the sequence have to satisfy $sumlimits_{k=0}^infty d(a_k,a_{k+1})<infty$?










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  • $begingroup$
    If the sum is infinite, then $r_m=infty$ for all $m$...
    $endgroup$
    – Mindlack
    Jan 19 at 11:10
















0












$begingroup$


Let $(M,d)$ be a metric space and $(a_n)subset M$ a sequence. Is it always true that if $r_m=sumlimits_{k=m}^infty d(a_k,a_{k+1})$ we have $limlimits_{mrightarrowinfty}r_m=0$?



$$r_m=sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{m-1}d(a_k,a_{k+1})xrightarrow[mrightarrowinfty]{}sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{infty}d(a_k,a_{k+1})=0$$



Is this always correct or does the sequence have to satisfy $sumlimits_{k=0}^infty d(a_k,a_{k+1})<infty$?










share|cite|improve this question









$endgroup$












  • $begingroup$
    If the sum is infinite, then $r_m=infty$ for all $m$...
    $endgroup$
    – Mindlack
    Jan 19 at 11:10














0












0








0





$begingroup$


Let $(M,d)$ be a metric space and $(a_n)subset M$ a sequence. Is it always true that if $r_m=sumlimits_{k=m}^infty d(a_k,a_{k+1})$ we have $limlimits_{mrightarrowinfty}r_m=0$?



$$r_m=sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{m-1}d(a_k,a_{k+1})xrightarrow[mrightarrowinfty]{}sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{infty}d(a_k,a_{k+1})=0$$



Is this always correct or does the sequence have to satisfy $sumlimits_{k=0}^infty d(a_k,a_{k+1})<infty$?










share|cite|improve this question









$endgroup$




Let $(M,d)$ be a metric space and $(a_n)subset M$ a sequence. Is it always true that if $r_m=sumlimits_{k=m}^infty d(a_k,a_{k+1})$ we have $limlimits_{mrightarrowinfty}r_m=0$?



$$r_m=sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{m-1}d(a_k,a_{k+1})xrightarrow[mrightarrowinfty]{}sumlimits_{k=0}^infty d(a_k,a_{k+1})-sumlimits_{k=0}^{infty}d(a_k,a_{k+1})=0$$



Is this always correct or does the sequence have to satisfy $sumlimits_{k=0}^infty d(a_k,a_{k+1})<infty$?







sequences-and-series metric-spaces






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asked Jan 19 at 10:44









John CataldoJohn Cataldo

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  • $begingroup$
    If the sum is infinite, then $r_m=infty$ for all $m$...
    $endgroup$
    – Mindlack
    Jan 19 at 11:10


















  • $begingroup$
    If the sum is infinite, then $r_m=infty$ for all $m$...
    $endgroup$
    – Mindlack
    Jan 19 at 11:10
















$begingroup$
If the sum is infinite, then $r_m=infty$ for all $m$...
$endgroup$
– Mindlack
Jan 19 at 11:10




$begingroup$
If the sum is infinite, then $r_m=infty$ for all $m$...
$endgroup$
– Mindlack
Jan 19 at 11:10










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If $M$ is real line with usual metric and $a_n=1+frac 1 2+cdots+frac 1 n$ then $r_m=infty$ for all $m$. If you assume that $sum d(a_n,a_{n+1})<infty$ then $r_m to 0$ as $m to infty$.






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    $begingroup$

    If $M$ is real line with usual metric and $a_n=1+frac 1 2+cdots+frac 1 n$ then $r_m=infty$ for all $m$. If you assume that $sum d(a_n,a_{n+1})<infty$ then $r_m to 0$ as $m to infty$.






    share|cite|improve this answer









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      0












      $begingroup$

      If $M$ is real line with usual metric and $a_n=1+frac 1 2+cdots+frac 1 n$ then $r_m=infty$ for all $m$. If you assume that $sum d(a_n,a_{n+1})<infty$ then $r_m to 0$ as $m to infty$.






      share|cite|improve this answer









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        $begingroup$

        If $M$ is real line with usual metric and $a_n=1+frac 1 2+cdots+frac 1 n$ then $r_m=infty$ for all $m$. If you assume that $sum d(a_n,a_{n+1})<infty$ then $r_m to 0$ as $m to infty$.






        share|cite|improve this answer









        $endgroup$



        If $M$ is real line with usual metric and $a_n=1+frac 1 2+cdots+frac 1 n$ then $r_m=infty$ for all $m$. If you assume that $sum d(a_n,a_{n+1})<infty$ then $r_m to 0$ as $m to infty$.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 19 at 11:44









        Kavi Rama MurthyKavi Rama Murthy

        63.7k42463




        63.7k42463






























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