# Matrix Identity: A*B != B*A but A*B = BT * AT

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I am looking for a matrix identity. The matrix product is of course not commutative. Do I remember correctly that the following identity holds true for arbitrary matrix products: A*B = Transpose(B) * Transpose(A) I mean we do this all the time when we use row major matrices in DirectX, I just want to be sure. Regards, -Dirk

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Quote:
 Original post by DonDickieDA*B = Transpose(B) * Transpose(A)

Actually, it is:
A*B = Transpose( Transpose(B)*Transpose(A) )

Why would you want to use DX matrices in the first place, just to not multiply the normal way, meaning predefined DX functions?
/def

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You are correct. The identy I was looking for was:
Tanspose( A * B ) = Transpose( B ) * Transpose( A )

I am working with the ODE and they used something similiar when
calculating J * W * JT ( Jacobian * inverse Mass * transposed Jacobian ) and
I was not sure what they were actually doing.

Thanks for the help...

-Dirk

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