I know that matrix multiplication is not commutative. And yet, I am taught that transformation matri

Llubanipo

Llubanipo

Answered question

2022-06-25

I know that matrix multiplication is not commutative. And yet, I am taught that transformation matrices can be composed to arrive at a single transformation. So then, suppose that I have 3 matrices - each representing a rotation about each axis of a 3D coordinate system. How can I be sure that I arrive at the correct result, if the order matters?

Answer & Explanation

Trey Ross

Trey Ross

Beginner2022-06-26Added 30 answers

You are combining two distinct concepts. In the generic case, given two matrices A,B, it is true that the order in which you list them before multiplying them matters - you wouldn't anticipate AB=BA to be true in the absence of additional information. Technically speaking, matrix multiplication might not be commutative.
When you have 3 or more matrices we can talk about a different kind of "order". If you multiply the three matrices to get the product ABC the question arises whether this means you multiply A and B to get another matrix X and then multiply X and C. Or should you multiply B and C to get another matrix Y and then multiply A and Y. The fact is, out of those two possibilities you always get the same result. It is in this sense that the "order doesn't matter" which you are talking about. The technical name for this is that matrix multiplication is associative.

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