In mathematics, a normed algebra A is an algebra over a field which has a sub-multiplicative norm:
∀ x , y ∈ A ‖ x y ‖ ≤ ‖ x ‖ ‖ y ‖ . {\displaystyle \forall x,y\in A\qquad \|xy\|\leq \|x\|\|y\|.}
Some authors require it to have a multiplicative identity 1A such that ‖1A‖ = 1.
See also
External reading "Normed Algebra". Encyclopaedia of Mathematics. Retrieved 20 May 2018.