- **Calculus & Beyond Homework**
(*http://www.physicsforums.com/forumdisplay.php?f=156*)

- - **Determine if this subset is compact**
(*http://www.physicsforums.com/showthread.php?t=403564*)

Determine if this subset is compact1. The problem statement, all variables and given/known dataLet [tex](X,d) = (C[0,1], d_\infty)[/tex], [tex]S_1[/tex] is the set of constant functions in [tex]B(0,1)[/tex], and [tex]S_2 = \{ f \in C[0,1] | \norm{f}_\infty = 1\}[/tex]. Are [tex]S_1[/tex] and [tex]S_2[/tex] compact? 2. Relevant equations3. The attempt at a solutionI am trying to use the Arzela - Ascoli theorem. For [tex]S_1[/tex], the set of functions with value in the ball (assuming that's what the question meant) [tex]B(0,1)[/tex] are bounded. They are also equicontinuous at all [tex] x \in [0,1] [/tex]. How do I show if the subset is closed or not? For [tex]S_2[/tex], how does the norm [tex]||f||_\infty = 1 [/tex] determine if the set is closed, bounded and equicontinuous? What is the norm [tex]||f||_\infty = 1 [/tex] defined as? |

Re: Determine if this subset is compactWell, first you have to understand the notation and definitions. [itex]d_\infty[/itex] is just the metric induced by the supremum norm:
[tex]\|f\|_\infty:=\sup_{x\in[0,1]} |f(x)|[/tex] |

Re: Determine if this subset is compactQuote:
outside [tex]S_1[/tex]. Therefore [tex]S_1[/tex] is not compact. For [tex]S_2[/tex], the metric space [tex]d_\infty(f,g) := \norm{f - g}_\infty[/tex] means that it is bounded, however it does not make [tex]S_2[/tex] equicontinuous. Is the subset closed? |

All times are GMT -5. The time now is 09:10 PM. |

Powered by vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.

© 2014 Physics Forums