# don't understand matrix

#### zentech

##### New member
Hi everybody, I have a simple question about matrices. I was reading a tutorial and in it the author was describing non-commutative nature of matrix multiplication and how it applied to the aviation designation of Euler matrices especially when they were all multiplied together: (roll x pitch) x yaw.

He says "is important to note that R(alpha_mat, beta_mat, gamma_mat) performs the roll first, then the pitch, and finally the yaw. If the order of these operations is changed, a different rotation matrix would result.". Matrices R list alpha_mat (yaw) and beta_mat (pitch) first, then finally gamma_mat which is the roll.
Simply put: it seems he doesn't list the matrices in the order he said they need to go. His is (yaw)(pitch) x (roll) when it should be (roll)(pitch) x yaw. It seems a contradiction in terms, however I suspect it might be my understanding.
Should be R(beta_mat, gamma_mat, alpha_mat)

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#### Romsek

##### Full Member
the product $$\displaystyle YPRx \text{ first applies roll (R), then pitch (P), then yaw (Y), as specified by the author}$$

#### zentech

##### New member
I knew it was simple - thank you.