How Do You Reverse a Vector Transformation?

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Discussion Overview

The discussion revolves around the process of reversing a vector transformation between coordinate systems. Participants explore the mathematical relationships involved in transforming vectors and the challenges encountered when attempting to revert to the original coordinates. The scope includes theoretical and mathematical reasoning related to vector transformations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a formula for transforming vector A from coordinate ei to ei', suggesting that to revert back, one might use Ai = aij Aj', but notes this does not yield the expected result.
  • Another participant explains that in an n-dimensional space, the transformation back to the original coordinate system involves the inverse of the transformation matrix, assuming it is non-singular.
  • A participant expresses confusion and requests a specific example involving given transformations of basis vectors and a vector t, noting discrepancies when attempting to revert to the original coordinates.
  • One participant claims to have found a transformed vector t' but does not clarify if this is correct, indicating uncertainty in the transformation process.
  • A later post poses a question about eliminating the transformation matrix A_{ij} to express the original vector in terms of the transformed vector, drawing an analogy to a simpler numerical relationship.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding the reversal of vector transformations, with some proposing methods while others remain confused. No consensus is reached on the correct approach to revert the transformations.

Contextual Notes

Participants mention specific transformations and matrices without providing complete definitions or assumptions, leading to potential ambiguities in the discussion. The mathematical steps involved in the transformations are not fully resolved.

Who May Find This Useful

Individuals interested in vector transformations, linear algebra, and those seeking to understand the complexities of coordinate system changes may find this discussion relevant.

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If we want to transform vector A from cooedinate ei to ei',
then this formula occur:
Aj' = aij Ai
But I have a question, if I have found all components of Aj', then I want to transform it back to Ai, what should I do?
I have tried Ai = aij Aj'
but it won't give me the same number.
Thanks...
 
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If, for example, your space is n-dimensional, then, given a particular coordinate system, each point can be written as an array of n numbers (a "vector"). The set of numbers aij, changing from one coordinate system to another can be written as a vector (and, assuming both are "valid" coordinates systems so they have the same dimension as the space, the matrix is non-singular). Then the transformation back the opposite way is just the inverse of that matrix.
 
I am still confused.
Can you give me an example please?
Let's say e1' = (2 e1 + 2 e2 + e3) /3
e2' = 1.4142 (e2 + e2)
e3' = 0.4714 (e1 + e2 + 4 e3)
and I have a vectro t = 10 e1 + 10 e2 - 20 e3
Can you transform it to e1', e2', and e3'?
I have done that, but when I rewrite it back to the original coordinate, it won't be like that.
Thanks...
 
By the way, I found that t' = 6.667 e1 + 47.14 e3
Is that OK?
Thanks...
 
You know that a'_{i} = A_{ij}a_{j}. You want a_{i} = \ldots. How can you get rid of the A_{ij} matrix on the right hand side using other matrices?

If you were working with just numbers and had b=ka, how would you work out a in terms of b? What's the matrix version of this?
 

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