World's most popular travel blog for travel bloggers.

# [Answers] About codes over $\mathbb{F}_2$

, ,
Problem Detail:

I was looking through these notes but I am not sure I can locate the answer to these questions of mine - it would be great if someone can just even point out what to look for!

• So any set of binary vectors can be seen as "code"?

• Let $M$ be a $d\times m$ matrix over $\mathbb{F}_2$ and let $X(M)$ be the graph on the binary vectors of length $d$, where two vectors are adjacent if their difference is a column of $M$. (does this mean that before comparing when one is taking a bit-wise difference of the vectors one is equating $-1$ to $1$ as would be inside $\mathbb{F}_2$?)

Does this above construction have a name? Any motivations?

• What is this NP-hard question about finding a "minimum weight code" among a set of binary vectors? Can someone kindly give the precise definition?

#### Answered By : Yuval Filmus

1. A binary code is a set of vectors in $\mathbb{F}_2^n$ for some $n$.

2. Presumably the context in which you encountered this construction is a motivation for it. It's a particular case of a more general construction known as a Cayley graph, though perhaps this particular case has a specific name. You are right that all arithmetic is done in $\mathbb{F}_2$.

3. There are several NP-complete problems related to codes; Madhu Sudan has an entire lecture on these. One of them is, given a generator matrix for a linear code, determine the minimum weight of a non-zero codeword (i.e., the minimum distance).

###### Best Answer from StackOverflow

Question Source : http://cs.stackexchange.com/questions/41033

3.2K people like this