What it means to be infinitely differentiable

  • Context: Graduate 
  • Thread starter Thread starter fred_91
  • Start date Start date
  • Tags Tags
    Differentiable Means
Click For Summary

Discussion Overview

The discussion revolves around the definitions and implications of being infinitely differentiable in the context of mathematical functions. Participants explore the nuances between being infinitely many times continuously differentiable and simply infinitely many times differentiable, particularly in relation to the concept of C^∞ functions.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that "infinitely many times continuously differentiable" and "infinitely many times differentiable" may not be equivalent, raising questions about the definition of C^∞.
  • One participant notes that being infinitely differentiable refers to a property at a specific point, emphasizing that the continuity of the (n-1)th derivative is necessary to obtain the nth derivative at that point.
  • Another participant points out that the operation of differentiating a function "infinitely many times" is considered undefined, clarifying that an "infinitely differentiable" function is one for which the Nth derivative exists for any finite integer N > 0.
  • A participant states that a differentiable function must be continuous.

Areas of Agreement / Disagreement

Participants express differing views on the equivalence of the terms related to infinite differentiability, indicating that the discussion remains unresolved with multiple competing interpretations.

Contextual Notes

There are limitations in the discussion regarding the definitions and assumptions surrounding differentiability and continuity, particularly in the context of infinite operations and their implications.

fred_91
Messages
38
Reaction score
0
<Moderator's note: Moved from a homework forum.>

1. Homework Statement

I am wondering if it is the same to say :

Function f is infinitely many times continuously differentiable
AND
Function f is infinitely many times differentiable

And if it is not the same, which one defines: C^infinity ?

Homework Equations

The Attempt at a Solution

 
Physics news on Phys.org
Infinitely differential C^{\infty} refers to a property at a particular point. However to get the nth derivative at that point, the (n-1)th derivative needs to be continuous at that point.
 
It's worth mentioning that to differentiate a function "infinitely many times" is an undefined operation. An "Infinitely differentiable" function is one whose Nth derivative exits for any finite integer N > 0.
 
A differentiable function is continuous.
 

Similar threads

  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 46 ·
2
Replies
46
Views
6K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K