# 15.2 Norms

 Page 1 / 1
This module will define a norm and give examples and properties of it.

## Introduction

This module will explain norms, a mathematical concept that provides a notion of the size of a vector. Specifically, the general definition of a norm will be discussed and discrete time signal norms will be presented.

## Norms

The norm of a vector is a real number that represents the "size" of the vector.

In $\mathbb{R}^{2}$ , we can define a norm to be a vectors geometric length.

$x=\left(\begin{array}{c}{x}_{0}\\ {x}_{1}\end{array}\right)$ , norm $(x)=\sqrt{{x}_{0}^{2}+{x}_{1}^{2}}$

Mathematically, a norm $(·)$ is just a function (taking a vector and returning a real number) that satisfies three rules.

To be a norm, $(·)$ must satisfy:

1. the norm of every vector is positive $\forall x, x\in S\colon (x)> 0$
2. scaling a vector scales the norm by the same amount $(\alpha x)=\left|\alpha \right|(x)$ for all vectors $x$ and scalars $\alpha$
3. Triangle Property: $(x+y)\le (x)+(y)$ for all vectors $x$ , $y$ . "The "size" of the sum of two vectors is less than or equal to the sum of their sizes"

A vector space with a well defined norm is called a normed vector space or normed linear space .

## Examples

$\mathbb{R}^{n}$ (or $\mathbb{C}^{n}$ ), $x=\left(\begin{array}{c}{x}_{0}\\ {x}_{1}\\ \dots \\ {x}_{n-1}\end{array}\right)$ , $(, x)=\sum_{i=0}^{n-1} \left|{x}_{i}\right|$ , $\mathbb{R}^{n}$ with this norm is called ${\ell }^{1}\left(\left[0,n-1\right]\right)$ .

$\mathbb{R}^{n}$ (or $\mathbb{C}^{n}$ ), with norm $(, x)=\sum_{i=0}^{n-1} \left|{x}_{i}\right|^{2}^{\left(\frac{1}{2}\right)}$ , $\mathbb{R}^{n}$ is called ${\ell }^{2}\left(\left[0,n-1\right]\right)$ (the usual "Euclidean"norm).

$\mathbb{R}^{n}$ (or $\mathbb{C}^{n}$ , with norm $()$ x i x i is called ${\ell }^{\infty }\left(\left[0,n-1\right]\right)$

## Spaces of sequences and functions

We can define similar norms for spaces of sequences and functions.

Discrete time signals = sequences of numbers $x(n)=\{\dots , {x}_{-2}, {x}_{-1}, {x}_{0}, {x}_{1}, {x}_{2}, \dots \}$

• $(, x(n))=\sum_{i=()}$ x i , $x(n)\in {\ell }^{1}\left(ℤ\right)\implies ((, x))$
• $(, x(n))=\sum_{i=()} ^{}$ x i 2 1 2 , $x(n)\in {\ell }^{2}\left(ℤ\right)\implies ((, x))$
• $(, x(n))=\sum_{i=()} ^{}$ x i p 1 p , $x(n)\in {\ell }^{p}\left(ℤ\right)\implies ((, x))$
• $()$ x n sup i | x [ i ] | , $x(n)\in {\ell }^{\infty }\left(ℤ\right)\implies (())$ x

For continuous time functions:

• $(, f(t))=\int_{()} \,d t^{}$ f t p 1 p , $f(t)\in {L}^{p}\left(ℝ\right)\implies ((, f(t)))$
• (On the interval) $(, f(t))=\int_{0}^{T} \left|f(t)\right|^{p}\,d t^{\left(\frac{1}{p}\right)}$ , $f(t)\in {L}^{p}\left(\left[0,T\right]\right)\implies ((, f(t)))$

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Got questions? Join the online conversation and get instant answers!