Euclidean unit ball
= Euclidean unit ball
{c}
{title2=$B_2^d=\{x\in\mathbb R^d:|x|\leq1\}$}
The <Euclidean unit ball> is the closed <unit ball> of the <Euclidean norm>, centered at zero. Its radial function is identically $1$, making it a natural reference body for <John ellipsoids> and <volume ratios>.