Suppose that{u1,u2, ,um} are non-zero pairwise orthogonal vectors

  • Context: Graduate 
  • Thread starter Thread starter squenshl
  • Start date Start date
  • Tags Tags
    Orthogonal Vectors
Click For Summary

Discussion Overview

The discussion revolves around the problem of demonstrating that for a set of non-zero pairwise orthogonal vectors {u1, u2, ..., um} in a subspace W of dimension n, the inequality m <= n holds. The scope includes theoretical reasoning and mathematical proof techniques.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant seeks direction on how to approach the proof regarding the relationship between the number of orthogonal vectors and the dimension of the subspace.
  • Another participant clarifies the notation, suggesting that the dot product is implied and emphasizes the importance of defining the vector space clearly.
  • A suggestion is made to start with a simple example, such as R^2, to understand why a pairwise orthogonal set must be smaller than the dimension of the subspace.
  • Further advice is given to consider the properties of a vector space of size N, including the implications for the number of elements in a basis and linear independence.
  • A participant expresses gratitude for the guidance but seeks further clarification on how to express their problem mathematically.
  • Another participant encourages the original poster to articulate their difficulties in mathematical terms and to consider the relationship between linear independence and orthogonality.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as the discussion includes various approaches and suggestions without settling on a single method or conclusion.

Contextual Notes

There are limitations regarding the clarity of notation and definitions, as well as the need for further exploration of the relationship between linear independence and orthogonality in the context of the proof.

squenshl
Messages
468
Reaction score
4
I need some direction. I don't have a clue where to start.
Suppose that{u1,u2,...,um} are non-zero pairwise orthogonal vectors (i.e., uj.ui=0 if i doesnt=j) of a subspace W of dimension n. Show that m<=n.
 
Physics news on Phys.org


I assume by dot you mean dot product / inner product? It helps if you are really clear about your notation -- eg is W a vector space, ring, module, etc.

Second, in general, one fruitful way to start proofs like this is to take a simple example which you understand well and look at why your theorem is true or false. So examine, say, R^2 and see why any pairwise orthogonal set must be smaller than the dimension of the subspace it is in. One example set might be the usual basis.

Third, generalize.

Another way to start is to think about what is special about a vector space of size N? You should know that N implies several things -- ie the number of elements in a basis, the largest possible linearly independent set, isomorphism to F^n where F is your field, etc.
 


Thanks that helps a lot.
So how would I start my notation to my particular problem and do it.
 


Huh? If you want to say in words what you're having trouble expressing in a mathematical way, I'll help, but you need to put in the work to solve this.

Think about the interaction between linear independence and orthogonality.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 4 ·
Replies
4
Views
7K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
22
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K