Cyclic codes

A cyclic code is associated to an irreducible polynomial over $\mathbb{F}$ which divides $x^n-1$.

For example, to get the $[7, 4, 3]$ cyclic code over $GF(2)$ having generator matrix

$$\left( \begin{array}{ccccccc} 1& 0& 0& 0& 1& 1& 0\\ 0& 1& 0... ... 0& 0& 1& 0& 1& 1& 1\\ 0& 0& 0& 1& 1& 0& 1 \end{array}\right)$$

R<x>:=PolynomialRing(GF(2));
g:=x^3+x+1;
Factorization(x^7-1);
C:=CyclicCode(7,g);
C;
G:=GeneratorMatrix(C);
G;

To get the parity check matrix, type H:=ParityCheckMatrix(C); Try IsCyclic(C);

To get the dimension of the code, type Dimension(C); To get its minimum distance, type MinimumDistance(C);

Exercise 5   Check if $x^2+1$ is a generating polynomial of a cyclic code of length $4$ over $GF(2)$. If so, find a basis for this code, as a vector space over $GF(2)$, and construct a parity check matrix.