\|The `\|` symbol is used as a delimiter in mathematical expressions, often representing a norm or absolute value. It is commonly used to denote the magnitude of a vector or the absolute value of a number.
The norm of a vector x in Euclidean space.
\|x\| = \sqrt{x_1^2 + x_2^2 + \cdots + x_n^2}The operator norm of a matrix A.
\|A\| = \max_{x \neq 0} \frac{\|Ax\|}{\|x\|}The L^p norm of a function f.
\|f\|_p = \left(\int |f(x)|^p \, dx \right)^{1/p}