# Norm v.s. absolute value.

1. Sep 18, 2011

### athrun200

I saw some books and say that norm is the absolute value in vector.

If it also means absolute value, why don't we use absolute value |$\vec{v}$| instead we use ||$\vec{v}$||?

2. Sep 18, 2011

### Alchemista

Absolute value is the usual norm for $\mathbb{R}$.
The euclidean norm is the usual norm for $\mathbb{R}^n$

While the euclidean norm is sometimes written using the same notation as absolute value, it is not the same thing. Furthermore, in the abstract a norm is not necessarily the euclidean norm.

http://en.wikipedia.org/wiki/Norm_(mathematics [Broken])

Last edited by a moderator: May 5, 2017
3. Sep 18, 2011

### HallsofIvy

Strictly speaking, as Alchemista said, "absolute value" only applies to numbers. "norm" applies to any vector space, whether $R^n$ or more abstract, even infinite dimensional vector spaces. Of course, the set of real numbers can be thought of as a one-dimensional vector space and then the "usual norm" is, the absolute value.

Because of that, you will occaisionaly see the term "absolute value" used for the general norm but that is not very good terminology.