3
$\begingroup$

Consider the metric space $(\mathbb{R}^{\mathbb{N}},d)$ where for $x,y\in\mathbb{R}^\mathbb{N}$ $$ d(x,y) = \sum_{n=1}^{\infty} 2^{- n} \frac{\bigvee_{k\leq n}\left|x_k-y_k\right|}{1 + \bigvee_{k\leq n} \left|x_k-y_k\right|}.$$ I am wondering if that metric is well-known in the context of the infinite-dimensional space $\mathbb{R}^\mathbb{N}$ and whether it has a name. Does it make the space $\mathbb{R}^{\mathbb N}$ complete?

  • 2
    What is $\bigvee_{n = 1}^{\infty} \left| x_n - y_n \right|$?2012-11-26
  • 0
    @MichaelGreinecker $\bigvee_n$ usually denotes $\sup_n$. And learner: What do you mean by $\mathbb R^\infty$? All sequences? Or only the finally zero ones?2012-11-26
  • 0
    @learner It is somewhat standard. But in that case, you do not really get a metric. The supremum can be infinite.2012-11-26
  • 0
    I apologize Michael, I made a mistake in the definition. I will correct it.2012-11-26
  • 2
    This seems like a near-duplicate of http://math.stackexchange.com/questions/21552/omega-space-of-all-sequences-with-frechet-metric/216332012-11-26
  • 0
    Yes, it seem like it metrizes the product topology (which could be done easier).2012-11-26

0 Answers 0