What is Spanning and its Relation to Dimensionality?

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Discussion Overview

The discussion revolves around the concept of spanning in vector spaces, particularly in relation to dimensionality. Participants explore the implications of the number of vectors in a set and their ability to span a given space, as well as specific problems related to proving relationships between spans of different sets of vectors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about spanning, noting that a set of five vectors cannot span M(2,3) while six or seven vectors can, given that the dimension of M(2,3) is 6.
  • Another participant clarifies that the span of a set of vectors is the vector space of minimal dimension containing those vectors, emphasizing that a 6-dimensional space cannot be spanned by only 5 vectors.
  • A participant poses a problem about proving that span{u,v} equals span{u,v,w} if w is an element of span{u,v} in R^n, seeking assistance on how to approach this proof.
  • Subsequent replies discuss the definitions of spans and suggest that the proof involves showing mutual inclusion of elements in the spans of the sets.
  • Some participants express difficulty in starting the proof and seek further help, indicating a collaborative effort to understand the problem.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of spanning and dimensionality, but the specific proof regarding the relationship between spans remains unresolved, with some participants struggling to articulate their approach.

Contextual Notes

Limitations include the participants' varying levels of understanding regarding the definitions and implications of spans, as well as the specific mathematical steps required to prove the relationship between the spans.

Who May Find This Useful

This discussion may be useful for students and individuals seeking to understand the concepts of spanning and dimensionality in vector spaces, as well as those looking for assistance with related mathematical proofs.

Saggittarius
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I'm a little confused on exactly what spanning is. For example, It's not possible for a set of five vectors to span M(2, 3), but it is possible for a set of six vectors or seven vectors. Why is this? I understand the dimension of M(2,3)=6. I just need a little bit more information on what spanning is.
 
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The span of a set of vectors is the vector space of minimal dimension that contains those vectors.

As you say you understand what dimension is - the size of a minimal spanning set - then it should now seem tautologous to say that a 6 dimension space cannot be spanned by 5 vectors: a set of 5 vectors can span a vector space of dimension *at most* 5.
 


o ok.. thanks so much!
 
Span

I have a problem. How do I prove that span{u,v} = span{u,v,w} if w is an element of the span{u,v), in R^n.
I don't know how to do this.
Any ideas anyone.
 


You use the definitions:

(a,b,c,d,e,f,g represent elements of the base field)

span(u,v) is the set of things of the form au+bv
span(u,v,w) is the set of things of the form cu+dv+ew
w is in span(u,v) means w=...?
 


Thanks for that.
I'm just having trouble getting started
 


I can't seem to do it.
Damn it's quite hard.
Any help would be greatly appreciated.
 


Have you written out what it is that you're trying to prove? You want to show that something that's in the span of {u,v} is in the span of {u,v,w} and vice versa.
 


Yes I have done that.
 
  • #10


Well, what is left to say? The result follows simply by rearranging the expressions involved.
 

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