Thread: How to understand the two vertical lines ||

Hello I read the following equation
Imageshack - log.gif
but I do not understand what the
|| (what ever is inside) ||2 (with the 2 as a small number -- called index?)


could you please help me understand what this is about?

I would like to thank you in advance for your help
Best Regards
Alex

That would be the 'length'

is a notation that represents the "length" of a vector . In your expression, is the vector whose length is being calculated.

Since "length" can be defined in a number of ways, the subscript indicates that the length is calculated using the Euclidean norm. So, means that you should find the length of the vector as defined by the Euclidean norm.

The Euclidean norm is the most intuitive definition of length. For example, if you have a vector , its Euclidean length would be . You can conceptualize this as the distance between the point and the origin.

Originally Posted by drumist

is a notation that represents the "length" of a vector . In your expression, is the vector whose length is being calculated.

Since "length" can be defined in a number of ways, the subscript indicates that the length is calculated using the Euclidean norm. So, means that you should find the length of the vector as defined by the Euclidean norm.

The Euclidean norm is the most intuitive definition of length. For example, if you have a vector , its Euclidean length would be . You can conceptualize this as the distance between the point and the origin.

I would like to thank you for your helpful post
So it is enough to say that it refers to the Euclidean distance. I am still wondering why some texts wants to make life that hard when there are always simple ways to express things.
Best Regards
Alex

What is so "hard" about that notation?

What level text was this? There is usually a list of symbols, either in the very front or very back of the text book for an introductory text. In a more advanced text, of course, you would be expected to already know standard notation.