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| author | Sebastiano Tronto <sebastiano.tronto@gmail.com> | 2019-04-19 11:38:07 +0200 |
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| committer | Sebastiano Tronto <sebastiano.tronto@gmail.com> | 2019-04-19 11:38:07 +0200 |
| commit | d794bad3364a7bf0c5ca12241d36a9ebb48c68d8 (patch) | |
| tree | b6960a33d407c9c1fbe583d3ceb8991332bdb921 /README.md | |
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| download | kummer-degrees-d794bad3364a7bf0c5ca12241d36a9ebb48c68d8.tar.gz kummer-degrees-d794bad3364a7bf0c5ca12241d36a9ebb48c68d8.zip | |
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| 1 | # Kummer Degrees | 1 | # Kummer Degrees |
| 2 | A SageMath script that computes the degrees of Kummer Extensions of the rational numbers. | 2 | A SageMath script that computes the degrees of Kummer Extensions of the rational numbers. |
| 3 | It contains the following useful functions: | ||
| 4 | |||
| 5 | +-----------------------+ | ||
| 6 | |TotalKummerFailure( G )| | ||
| 7 | +-----------------------+ | ||
| 8 | |||
| 9 | Outputs the description of the failure of maximality | ||
| 10 | for all possible values of M and N. Here G is given as a list of generators | ||
| 11 | (not necessarily a basis). G can also contain torsion. If G = <-1>, the program | ||
| 12 | stops immediately. | ||
| 13 | |||
| 14 | Example: | ||
| 15 | |||
| 16 | sage: TotalKummerFailure([-36,12,-1]) | ||
| 17 | output: | ||
| 18 | M_0 = 24 | ||
| 19 | N_0 = 8 | ||
| 20 | |||
| 21 | The following table shows the total failure of Kummer degrees in | ||
| 22 | case the quotient M/N is EVEN. | ||
| 23 | Columns correspond to values of M, rows to values of N | ||
| 24 | |||
| 25 | The degree of the Kummer extension (M,N) can be extracted by taking | ||
| 26 | the value f (failure) of the entry at (gcd(N,N0),gcd(M,M0)) and | ||
| 27 | simply computing ed(M,N) / f, where ed(M,N) is the expected degree | ||
| 28 | of the Kummer extension. | ||
| 29 | In this case (-1 is in G), we have ed(M,N) = 2^e*phi(M)*N^r, | ||
| 30 | where e=1 if N is even and e=0 if N is odd. | ||
| 31 | where r is the rank of G. | ||
| 32 | |||
| 33 | | 1 2 3 4 6 8 12 24 | ||
| 34 | - - - - - - - - - - | ||
| 35 | 1 | 1 1 1 1 1 1 1 1 | ||
| 36 | 2 | 4 4 4 4 4 4 8 8 | ||
| 37 | 4 | 4 4 4 4 4 8 8 16 | ||
| 38 | 8 | 8 8 8 8 8 16 16 32 | ||
| 39 | |||
| 40 | The following table shows the total failure of Kummer degrees in | ||
| 41 | case the quotient M/N is ODD. | ||
| 42 | This table can be read exactly as the first one. | ||
| 43 | |||
| 44 | | 1 2 3 4 6 8 12 24 | ||
| 45 | - - - - - - - - - - | ||
| 46 | 1 | 1 1 1 1 1 1 1 1 | ||
| 47 | 2 | 2 2 2 2 4 2 4 4 | ||
| 48 | 4 | 2 2 2 4 4 4 8 8 | ||
| 49 | 8 | 4 4 4 8 8 8 16 16 | ||
| 50 | |||
| 51 | ------------------------------------------------------------------------------- | ||
| 52 | |||
| 53 | +-----------------------+ | ||
| 54 | |KummerDegree( G, M, N )| | ||
| 55 | +-----------------------+ | ||
| 56 | |||
| 57 | Returns the degree of the Kummer extension Q_{M,N}. Again, G is given simply as | ||
| 58 | a list of generators and it may contain torsion. | ||
| 59 | |||
| 60 | sage: KummerDegree([-36,12,-1],120,24) | ||
| 61 | output: | ||
| 62 | 2304 | ||
| 63 | |||
| 64 | ------------------------------------------------------------------------------- | ||
