The double bar symbol is used to denote certain kinds of norms in mathematics (e.g., or ). It is also used to denote parallel lines, as in , and in an older notation for the covariant derivative. In this work, the notation or is reserved for matrix and function norms, respectively.

# Double Bar

## See also

Bar, Covariant Derivative, Norm, Matrix Norm, Parallel, Single Bar## Explore with Wolfram|Alpha

## References

Bringhurst, R.*The Elements of Typographic Style, 2nd ed.*Point Roberts, WA: Hartley and Marks, p. 277, 1997.

## Referenced on Wolfram|Alpha

Double Bar## Cite this as:

Weisstein, Eric W. "Double Bar." From
*MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/DoubleBar.html