Hey Guys,

I am trying to understand quaternions.

I am using a book called: “Mathematics for Computer Graphics” and the NEHE-Tutorial.

Nehe_Quaternion

But after looking closely i have seen that they have 2 different Quaternion definitions.

The + changes to -, when the position of two coefficients is changed.

It would make sense, if this were two imaginary digits but s is real.

Can i assume that it is the same?

But i dont understand why the unsign is changing, when i multiplicate an imaginary with a real digit.

I thought that the multiplication of two imaginary digits is not commutative.

Is it the same with imaginary digits and real ones?

Thanks

```
BOOK | NEHE | Difference |
------------------------------------------------------------
M11 = 1 - 2(yy + zz) | 1 - 2(yy + zz) |
M12 = 2(xy - sz) | 2(xy + zs) | X
M13 = 2(xz + sy) | 2(xz - ys) | X
M14 = 0 | 0 |
------------------------------------------------------------
M21 = 2(xy + sz) | 2(xy - zs) | X
M22 = 1 - 2(xx + zz) | 1 - 2(xx + zz) |
M23 = 2(yz - sx) | 2(zy + xs ) | X
M24 = 0 | 0 |
------------------------------------------------------------
M31 = 2(xz - sy) | 2(xz + ys) | X
M32 = 2(yz + sx) | 2(yz - xs) | X
M33 = 1 - 2(xx + yy) | 1 - 2( xx + yy ) |
M34 = 0 | 0 |
------------------------------------------------------------
M41 = 0 | |
M42 = 0 | |
M43 = 0 | |
M44 = 1 | |
------------------------------------------------------------
```