Linearly independent but not orthogonal, how come?

Click For Summary

Discussion Overview

The discussion revolves around the concepts of linear independence and orthogonality of vectors in linear algebra. Participants explore the definitions and relationships between these two properties, particularly in the context of the Gram-Schmidt process and examples in R².

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether linear independence implies orthogonality, seeking clarification on the definitions of both terms.
  • Another participant explains that linear independence means no vector in the set can be expressed as a linear combination of the others, while orthogonality means the dot product of any two vectors is zero.
  • A participant asserts that while orthogonal vectors are linearly independent, not all linearly independent vectors are orthogonal, providing the example of the vector i+j.
  • Another example is given in R² with the vectors <1, 0> and <1, 1>, illustrating that they are linearly independent but not orthogonal, as they form a 45-degree angle.
  • It is reiterated that the implication only goes one way: orthogonal vectors are linearly independent, but linear independence does not guarantee orthogonality.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of linear independence and orthogonality, but there is some confusion regarding the implications of these definitions, particularly whether linear independence necessarily leads to orthogonality.

Contextual Notes

Participants rely on specific examples to illustrate their points, which may depend on the dimensionality of the vector space being discussed. The discussion does not resolve the confusion for all participants.

physlad
Messages
19
Reaction score
0
Hi everyone, I was reading about Gram-Schmidt process of converting two linearly independent vectors into orthogonal basis. But, as I understand, if two vectors are linearly independent then they are orthogonal! isn't that right??
Could anybody explain... please.
 
Physics news on Phys.org
No. What does it mean to have a set of linearly independent vectors? What does it mean to have a set of orthogonal vectors?
 
As I understand, a set of linearly independent vectors means that it is not possible to write any of them in terms of the others.
a set of orthogonal vectors means that the dot product of any two of them is zero. which in turn means that they are independent of each other, right? that's what confuses me.
 
Vectors which are orthogonal to each other are linearly independent. But this does not imply that all linearly independent vectors are also orthogonal. Take i+j for example. The linear span of that i+j is k(i+j) for all real values of k. and you can visualise it as the vector stretching along the x-y plane in a northeast and southwest direction. However, there does not exist any value of k such that k(i+j) = i. i and i+j are linearly independent, but not orthogonal.
 
For example, in R2, the vectors <1, 0> and <1, 1,> are independent since the only way to have a<1, 0>+ b<1, 1>= 0 is to have a= 0 and b= 0. But they are NOT "orthogonal"- the angle between them is 45 degrees, not 90.

As Defennndeer said, if two vectors are orthogonal, then they are linearly independent but it does NOT work the other way.
 

Similar threads

  • · Replies 14 ·
Replies
14
Views
4K
  • · Replies 9 ·
Replies
9
Views
4K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 9 ·
Replies
9
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
2
Views
1K
  • · Replies 23 ·
Replies
23
Views
3K
  • · Replies 9 ·
Replies
9
Views
5K