How to compute the rotation matrix

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Discussion Overview

The discussion revolves around computing a rotation matrix from two given matrices, X and X0, both of size 4x3. Participants explore the concept of rotation in the context of coordinate transformations and the mathematical requirements for such transformations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asks how to compute the rotation matrix R from the matrices X and X0, given that X = RX0.
  • Another participant points out that a rotation matrix must be square and questions the dimensions of the matrices involved.
  • A participant clarifies that in the context of real matrices, a rotation typically refers to an orthogonal matrix with a determinant of 1, and questions whether the matrices satisfy the condition A^T A = B^T B for such a rotation to exist.
  • There is mention of using Gram-Schmidt orthogonalization to find R, but uncertainty remains about its applicability to the problem.
  • Another participant introduces the concept of Helmert transformation as a potential solution, indicating differing approaches to the problem.
  • One participant emphasizes the need for a clear problem statement, particularly regarding the definition of "rotation" in four-dimensional space.

Areas of Agreement / Disagreement

Participants express differing views on the definition of rotation in this context and the methods to compute the rotation matrix. There is no consensus on the appropriate approach or the conditions under which a solution exists.

Contextual Notes

Participants note that the matrices are not square and discuss the implications of this for finding a rotation matrix. The discussion includes references to specific mathematical conditions and methods, but these remain unresolved.

Renoald
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Hai , I have two matrix , let say X=[ A1 A2 A3
A4 A5 A5
A7 A8 A9
A10 A11 A12]
and X0=[B1 B2 B3
B4 B5 B6
B7 B8 B9
B10 B11 B12]

Can anyone show me how to compute the rotation matrix from X and X0 ?
Thank You
 
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Hey Renoald and welcome to the forums.

One problem that you have is that a rotation matrix preserves the dimension and is a basis which means that the matrix has to be square (even if some values don't contribute in the form of zero entries).

I think it would be helpful if you gave the exact dimensions of your matrices for X and X0. If these are vectors in a Euclidean space, then this is a very well understood problem, but if they are matrices then we will need a more general result.

So let's say X is a matrix with 3 rows and 2 columns, X will be a 3x2 matrix.
 
Hai , Thank You for reply!
The dimension of X and X0 is 4 x 3 ( Matrix form) and This is not a square matrix.
Let Say X=RX0 , then the rotation matrix is R . How to compute the R ?
Thank You ...
 
I am afraid you are going to have to explain what you mean by "rotating" one matrix to another.
 
Hi Renoald.

In \mathbb R^n the term "rotation" usually means an orthogonal matrix with the determinant 1 (the determinant of an orthogonal matrix is always 1 or -1).

So, as far as I understand your question is: given two 4\times 3 matrices A and B find a rotation (an orthogonal matrix with determinant 1) R such that B=RA. And your matrices have real entries. Am I correct here?

Note that such R does not always exists: for 2 real matrices A and B one can find an orthogonal matrix R such that B=RA if and only if A^T A =B^T B, where A^T is the transpose of A. So I assume your matrices satisfy this condition; if not, you are lucky, because such R does not exists, and you do not have to do anything :)

Probably the easiest way to find R is to apply Gram-Schmidt orthogonalization to the columns of one of the matrices (say A). If you know what it is, I can tell you what to do; if not, you have to learn it first.
 
Hai , thank you for the reply.
example i give here is what called as coordinate transformation.
I not sure Gram-Schmidt orthogonalization can used to resolve this problem or not !
as what i search by google , the solution given is Helmert transformation.
Any one have idea about this ?
 
Renoald,
if you want to get help, then STATE the problem first.

Am I correct, that translated to the mathematical language you problem can be stated like that:
given two 4×3 matrices A and B (with real entries) find a rotation (an orthogonal matrix with determinant 1) R such that B=RA?

If that is the statement, then the problem CAN be solved using Hilbert-Schmidt orthogonalization.

If that is not the statement, you should STATE the problem first: in particular, what do you mean by rotation in 4-dimensional space?
 

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