Can the Inverse of an Inner Product Be Described as a Function of Two Vectors?

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Discussion Overview

The discussion revolves around the possibility of expressing one vector as a function of another vector and a scalar, specifically in the context of inner products. It touches on theoretical aspects of vector relationships and applications in vortex dynamics using the law of Biot and Savart.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether a vector \( a \) can be expressed as a function of another vector \( b \) and a scalar \( c \) derived from their inner product.
  • Another participant argues that \( a \) cannot be uniquely determined by \( b \) and \( c \) due to the existence of orthogonal vectors that can be added to \( a \) without changing the inner product result.
  • A further contribution emphasizes that the solution to the equation \( a \cdot b = c \) is not unique, providing an example with an orthogonal vector \( d \).
  • A participant introduces a practical application involving vortex dynamics, expressing a desire to rewrite the circulation equation to relate vorticity and velocity fields, but expresses uncertainty about the feasibility of this approach based on earlier responses.
  • Another participant claims to have resolved their issue by determining a vector \( w \) in relation to its magnitude and direction, suggesting a method for expressing the vector in terms of its components.

Areas of Agreement / Disagreement

Participants generally disagree on the ability to express vector \( a \) as a function of \( b \) and \( c \), with some asserting that it is not possible due to non-uniqueness, while others explore related applications in vortex dynamics without reaching a consensus on the theoretical question.

Contextual Notes

The discussion includes assumptions about orthogonality and the uniqueness of vector representations, which may not be fully explored or defined. The application of the law of Biot and Savart in vortex dynamics introduces additional complexity that remains unresolved.

Who May Find This Useful

Readers interested in vector calculus, inner product spaces, vortex dynamics, and applications of the law of Biot and Savart may find this discussion relevant.

steem84
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my question is:

if a.b=c

with
a=any vector
b=any vector
.=inner product
c=resulting scalar

is there a way to describe a=f(b,c)?

Thanks
 
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No. a isn't completely determined by b and c, since you can replace a with a+d in your first equation, if d is orthogonal to b.
 
No. Think of it this way: Suppose you find vectors a and d such that a.b = c and d.b=0 (i.e., d is orthogonal to b). Then for any scalar k, (a+k*d).b=c also. In other words, the solution to a.b=c is not unique.
 
Ok thanks!

but it did not solve my problem regarding vortex dynamics...

I would like to use the the law of Biot and Savart to determine the velocity field induced by a vortex filament. I am trying to do this by rewriting the equation of the circulation to a function for the vorticity.

To do this, I am using the Dirac Delta function for another integral for the circulation. This way i can equal the two integrands. But from that expression I would like to write the vorticity as a function of the rest (to substitute it in Biot ans Savart). But from your explanations I see that this is not possible??
 

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already solved it...

w.n = the magnitude of the vector=length(w)
x=f(s)
dx/ds / length(dx/ds) = unity direction of the vector

so the vector is w is determined to be (w.n)*(dx/ds / length(dx/ds))
 

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