Inner Product Space of two orthogonal Vectors is 0 , Is this defined as it is ?

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Discussion Overview

The discussion revolves around the definition and properties of orthogonality in inner product spaces, particularly focusing on whether the inner product of two orthogonal vectors being zero is a definition or can be proven. The scope includes theoretical aspects of inner product spaces and the implications of these definitions in higher dimensions.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the inner product of two orthogonal vectors is defined to be zero, questioning whether this is merely a definition or can be proven.
  • Others argue that orthogonality is defined by the condition that the inner product is zero, suggesting that the definition is foundational rather than a provable statement.
  • One participant mentions that in lower-dimensional spaces, such as R² or R³, orthogonality can be understood geometrically, but in higher dimensions, it is simpler to adopt the definition that the inner product being zero indicates orthogonality.
  • A later reply introduces a related question about an operator T in a complex inner product space, raising concerns about the existence of orthogonality in n-dimensional vectors and the implications of = 0.

Areas of Agreement / Disagreement

Participants express disagreement regarding whether the condition of orthogonality being defined as an inner product of zero is a definitional matter or something that can be proven. The discussion remains unresolved with multiple competing views on the nature of orthogonality in inner product spaces.

Contextual Notes

Participants highlight the potential confusion regarding the definitions and properties of orthogonality in different dimensions and the implications of operators in complex inner product spaces, but do not resolve these issues.

vish_maths
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This may be a very silly question, but still apologies, I read in Sheldon Axler, that the inner product of two orthogonal vectors is DEFINED to be 0.
Let u,v belong to C^n. I am unable to find a direction of proof which proves that for an nth dimension vector space, if u perp. to v, then <u,v> = 0
Is it really just defined ? Or it can be proved to be 0 ?
 
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vish_maths said:
This may be a very silly question, but still apologies, I read in Sheldon Axler, that the inner product of two orthogonal vectors is DEFINED to be 0.

This is not correct. Rather, we define two vectors to be orthogonal if their inner product is 0.
So given u,v\in \mathbb{C}^n, we say that u and v are orthogonal iff <u,v>=0. This is a definition.
 
It can be shown, in R2 or R3, where we have a geometric definition of "orthogonal", that two vectors are orthogonal if and only if their dot product is 0. For higher dimension Euclidean spaces or more general vector spaces, it is simplest to take "inner product is 0" as the definition of "orthogonal".
 
Thanks a lot :). There has been just one more question which has been lingering in my mind.

If V is a complex inner product space and T is an operator on V such that <Tv,v> = 0 for all v belongs to V. Then T =0.
Though, it's proof is somewhat convincing , it has left me confused about
a) the existence of orthogonality in n dimensional vectors belong to C^n
b) if the answer above is yes, then why can't Tv be orthogonal to v. ( even if it's not visual, I mean in the mathematical sense)
 

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