# galois.conway_poly¶

galois.conway_poly(characteristic, degree)

Returns the Conway polynomial $$C_{p,m}(x)$$ over $$\mathrm{GF}(p)$$ with degree $$m$$.

Parameters
• characteristic (int) – The prime characteristic $$p$$ of the field $$\mathrm{GF}(p)$$ that the polynomial is over.

• degree (int) – The degree $$m$$ of the Conway polynomial.

Returns

The degree-$$m$$ Conway polynomial $$C_{p,m}(x)$$ over $$\mathrm{GF}(p)$$.

Return type

galois.Poly

Raises

LookupError – If the Conway polynomial $$C_{p,m}(x)$$ is not found in Frank Luebeck’s database.

Notes

A Conway polynomial is a an irreducible and primitive polynomial over $$\mathrm{GF}(p)$$ that provides a standard representation of $$\mathrm{GF}(p^m)$$ as a splitting field of $$C_{p,m}(x)$$. Conway polynomials provide compatability between fields and their subfields, and hence are the common way to represent extension fields.

The Conway polynomial $$C_{p,m}(x)$$ is defined as the lexicographically-minimal monic primitive polynomial of degree $$m$$ over $$\mathrm{GF}(p)$$ that is compatible with all $$C_{p,n}(x)$$ for $$n$$ dividing $$m$$.

This function uses Frank Luebeck’s Conway polynomial database for fast lookup, not construction.

Examples

Notice galois.primitive_poly() returns the lexicographically-minimal primitive polynomial, where galois.conway_poly() returns the lexicographically-minimal primitive polynomial that is consistent with smaller Conway polynomials, which is not necessarily the same.

In [1]: galois.primitive_poly(2, 4)
Out[1]: Poly(x^4 + x + 1, GF(2))

In [2]: galois.conway_poly(2, 4)
Out[2]: Poly(x^4 + x + 1, GF(2))

In [3]: galois.primitive_poly(7, 10)
Out[3]: Poly(x^10 + 5x^2 + x + 5, GF(7))

In [4]: galois.conway_poly(7, 10)
Out[4]: Poly(x^10 + x^6 + x^5 + 4x^4 + x^3 + 2x^2 + 3x + 3, GF(7))