Definition:Quaternion/Algebra over Field
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Definition
An algebra of quaternions can be defined over any field as follows:
Let $\mathbb K$ be a field, and $a$, $b \in \mathbb K$.
Define the quaternion algebra $\left\langle{ a,b }\right\rangle_\mathbb K$ to be the $\mathbb K$-vector space with basis $\{1, i, j, k\}$ subject to:
- $i^2 = a$
- $j^2 = b$
- $ij = k = -ji$
Formally this could be achieved as a multiplicative presentation of a suitable group, or as a linear subspace of a finite extension of $\mathbb K$.
Taking $\mathbb K = \R$ and $a = b = -1$ we see that this generalises Hamilton's quaternions.