Similarity transformation of an orthogonal matrix A transformation T represented by an orthog

glycleWogry

glycleWogry

Answered question

2022-06-05

Similarity transformation of an orthogonal matrix
A transformation T represented by an orthogonal matrix A , so A T A = I. This transformation leaves norm unchanged.
I do a basis change using a matrix B which isn't orthogonal , then the form of the transformation changes to B 1 A B in the new basis( A similarity transformation).
Therefore B 1 A B. [ B 1 A B ] T = I.
This suggests that B T B = I which means it is orthogonal, but that is a contradiction.

Answer & Explanation

hildiadau0o

hildiadau0o

Beginner2022-06-06Added 21 answers

A transformation A is orthogonal iff its matrix representation is orthogonal with respect to an standard orthogonal basis. And the transition matrix between two standard orthogonal bases must be orthogonal.
B 1 = { e 1 , , e n }, B 2 = { f 1 , , f n } are two standard orthogonal bases. A 1 and A 2 are representations of A with respect to B 1 , B 2 . Then A 1 , A 2 are orthogonal matrices.
A ( e i ) = the  i th colume of  A 1 ; A ( f i ) = the  i th colume of  A 2
If P is the transition matrix between B 1 and B 2 ( that is ( e 1 , , e n ) = ( f 1 , , f n ) P), then P is orthogonal.

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