(AB)^T = (B^T*A^T) proof help

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Chris
Chris on 3 Apr 2015
Answered: Chris on 3 Apr 2015
As the tittle indicates, i need help in proving the following within Matlab: (AB)^T = (B^T*A^T).
A=[1 8 5 4 ; 5 4 1 2; 4 1 2 5; 4 4 1 5],
B=[ 7 8 4 5; 7 4 5 6; 7 4 1 2; 9 4 1 2]
B and A are examples

Accepted Answer

James Tursa
James Tursa on 3 Apr 2015
Transposing in MATLAB is accomplished with the ' and .' operators. The ' operator is actually conjugate transpose and the .' is transpose without conjugate. For real inputs, ' does the same thing as .'
So for you case, replace the ^T notation with ' and then put in a * between A and B, and then you can show that the results match for any particular example.

More Answers (2)

Mischa Kim
Mischa Kim on 3 Apr 2015
Edited: Mischa Kim on 3 Apr 2015
Chris, you could simply do
>> A = [1 8 5 4 ; 5 4 1 2; 4 1 2 5; 4 4 1 5];
>> B = [ 7 8 4 5; 7 4 5 6; 7 4 1 2; 9 4 1 2];
>> (A*B)' - B'*A'
ans =
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
The prime does the transposing.

Chris
Chris on 3 Apr 2015
Wow, thankyou both very much! Both answers make clear sence and a very quick reply.

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