Differentitation - Why open set?

  • Thread starter thejinx0r
  • Start date
  • Tags
    Set
In summary, when defining a mapping f: U\subset R^n \rightharpoonup R^m, the domain U must be open in order for the derivative of f to exist at a point. If the domain is closed, we can only define a one-sided derivative. This is similar to the concept in Calculus I where the point of interest must be in the interior of the domain for the derivative to exist.
  • #1
thejinx0r
27
0
Hey guys,

why is it that when we define [tex]f:U\subset R^n \rightharpoonup R^m[/tex], why does U have to be open?
what happens if it's closed?

Thanks
 
Physics news on Phys.org
  • #2
I am a bit confused. Your title is "Differentiation- Why open set?" but you don't mention differentiation in the body.

If you are asking about mappings in general, no U does not have to be open. But if you are asking about points at which you can define the derivative of f, that's a different story.

Think about what happens in the "Calculus I", R1 case. The derivative of f(x), at x= a, is defined by
[tex]\lim_{h\rightarrow 0} \frac{f(a+h)- f(a)}{h}[/tex]
In order for that to exist, f(a+ h) has to be defined for all h close to 0- positive or negative. And that means that a has to be in the interior of some interval on which f is defined. If a is on the boundary, we can only define the "one sided derivative", using a one sided limit.

Now, in the more general, n dimensional, case, we have to be able to define f(x) for all x close to a. In other words, a must be an interior point of the domain of f. The set of all interior points of a set is, of course, an open set.
 
  • #3
oops... my bad.
Was trying to find an answer in my textbook as I wrote that question.

Nothing about it in there, but thanks a lot :)
 
Last edited:

FAQ: Differentitation - Why open set?

What is the purpose of differentiating an open set?

The main purpose of differentiating an open set is to identify and understand the behavior of a function or equation at a specific point. It allows us to determine the slope or rate of change of a function at that point, which is useful in many applications such as optimization and curve fitting.

How does an open set differ from a closed set?

An open set is a set that does not include its boundary points, while a closed set includes all of its boundary points. In other words, an open set is "open" because it does not contain its endpoints, while a closed set is "closed" because it includes its endpoints. This distinction is important in mathematical analysis and topology.

What is the concept of limit in an open set?

In an open set, the limit of a function at a point is defined as the value that the function approaches as the input approaches that point. This concept is crucial in understanding the behavior of a function at a specific point and is used to define important concepts such as continuity and differentiability.

Why is the concept of open sets important in topology?

In topology, open sets are used to define the topology or "shape" of a space. The properties of open sets, such as being closed under unions and intersections, allow us to define concepts such as connectedness and compactness, which are crucial in understanding the structure of a space.

How is the concept of differentiation related to open sets?

Differentiation is closely related to open sets because it relies on the concept of limits, which in turn relies on the openness of a set. The definition of a derivative involves taking a limit as the input approaches a point, which can only be done in an open set. Therefore, differentiation is only defined in open sets, making the concept of open sets crucial in understanding differentiation.

Similar threads

Back
Top