Cohomology of group number 388 of order 128

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General information on the group

  • The group has 3 minimal generators and exponent 8.
  • It is non-abelian.
  • It has p-Rank 3.
  • Its center has rank 2.
  • It has 3 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 3.

Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 3 and depth 3.
  • The depth exceeds the Duflot bound, which is 2.
  • The Poincaré series is
    ( − 1) · (t2  −  t  +  1) · (t2  +  t  +  1)
    (t  −  1)3 · (t2  +  1)2
  • The a-invariants are -∞,-∞,-∞,-3. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 11 minimal generators of maximal degree 5:

  1. b_1_0, an element of degree 1
  2. b_1_1, an element of degree 1
  3. b_1_2, an element of degree 1
  4. a_2_1, a nilpotent element of degree 2
  5. b_3_5, an element of degree 3
  6. b_3_6, an element of degree 3
  7. b_4_7, an element of degree 4
  8. b_4_8, an element of degree 4
  9. c_4_9, a Duflot regular element of degree 4
  10. c_4_10, a Duflot regular element of degree 4
  11. b_5_16, an element of degree 5

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Ring relations

There are 35 minimal relations of maximal degree 10:

  1. b_1_0·b_1_1
  2. b_1_0·b_1_2
  3. a_2_1·b_1_2
  4. a_2_1·b_1_0
  5. b_1_12·b_1_2 + a_2_1·b_1_1
  6. a_2_12
  7. b_1_2·b_3_5
  8. b_1_1·b_3_5 + a_2_1·b_1_12
  9. b_1_2·b_3_6
  10. b_1_1·b_3_6
  11. a_2_1·b_3_5
  12. a_2_1·b_3_6
  13. b_4_7·b_1_0
  14. b_4_8·b_1_0
  15. b_1_15 + b_4_8·b_1_1 + b_4_7·b_1_2 + b_4_7·b_1_1
  16. b_3_52 + c_4_9·b_1_02
  17. b_3_62 + b_3_52 + c_4_10·b_1_02
  18. b_4_7·b_1_1·b_1_2 + a_2_1·b_4_7
  19. a_2_1·b_1_14 + a_2_1·b_4_8 + a_2_1·b_4_7
  20. b_1_2·b_5_16 + b_4_7·b_1_22 + a_2_1·b_4_7 + c_4_10·b_1_22
  21. b_3_62 + b_3_5·b_3_6 + b_3_52 + b_1_0·b_5_16
  22. b_1_1·b_5_16 + b_4_7·b_1_12 + a_2_1·b_1_14 + c_4_10·b_1_1·b_1_2
  23. b_4_7·b_3_5 + a_2_1·b_4_7·b_1_1
  24. b_4_7·b_3_6
  25. b_4_8·b_3_5 + a_2_1·b_4_8·b_1_1
  26. b_4_8·b_3_6
  27. a_2_1·b_5_16 + a_2_1·b_4_7·b_1_1
  28. b_4_7·b_1_14 + b_4_72 + a_2_1·b_4_8·b_1_12 + a_2_1·b_4_7·b_1_12 + c_4_9·b_1_14
  29. b_4_7·b_1_14 + b_4_7·b_4_8 + b_4_72 + a_2_1·b_4_7·b_1_12 + c_4_10·b_1_1·b_1_23
       + a_2_1·c_4_9·b_1_12
  30. b_4_8·b_1_14 + b_4_82 + b_4_7·b_1_24 + b_4_7·b_1_14 + b_4_72
       + a_2_1·b_4_7·b_1_12 + c_4_10·b_1_24
  31. b_3_5·b_5_16 + a_2_1·b_4_7·b_1_12 + c_4_10·b_1_0·b_3_5 + c_4_9·b_1_0·b_3_6
  32. b_3_6·b_5_16 + c_4_10·b_1_0·b_3_6 + c_4_10·b_1_0·b_3_5 + c_4_9·b_1_0·b_3_5
  33. b_4_7·b_5_16 + b_4_72·b_1_1 + a_2_1·b_4_7·b_1_13 + b_4_7·c_4_10·b_1_2
  34. b_4_8·b_5_16 + c_4_10·b_1_1·b_1_24 + b_4_8·c_4_10·b_1_2 + b_4_8·c_4_9·b_1_1
       + b_4_7·c_4_9·b_1_2 + b_4_7·c_4_9·b_1_1 + a_2_1·c_4_9·b_1_13
  35. b_5_162 + b_4_72·b_1_12 + c_4_102·b_1_22 + c_4_102·b_1_02
       + c_4_9·c_4_10·b_1_02 + c_4_92·b_1_02

About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 128

Data used for Benson′s test

  • Benson′s completion test succeeded in degree 10.
  • The completion test was perfect: It applied in the last degree in which a generator or relation was found.
  • The following is a filter regular homogeneous system of parameters:
    1. c_4_9, a Duflot regular element of degree 4
    2. c_4_10, a Duflot regular element of degree 4
    3. b_1_22 + b_1_12 + b_1_02, an element of degree 2
  • The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 7].
  • The filter degree type of any filter regular HSOP is [-1, -2, -3, -3].

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Restriction maps

Restriction map to the greatest central el. ab. subgp., which is of rank 2

  1. b_1_0 → 0, an element of degree 1
  2. b_1_1 → 0, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. a_2_1 → 0, an element of degree 2
  5. b_3_5 → 0, an element of degree 3
  6. b_3_6 → 0, an element of degree 3
  7. b_4_7 → 0, an element of degree 4
  8. b_4_8 → 0, an element of degree 4
  9. c_4_9 → c_1_14 + c_1_04, an element of degree 4
  10. c_4_10 → c_1_14, an element of degree 4
  11. b_5_16 → 0, an element of degree 5

Restriction map to a maximal el. ab. subgp. of rank 3

  1. b_1_0 → c_1_2, an element of degree 1
  2. b_1_1 → 0, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. a_2_1 → 0, an element of degree 2
  5. b_3_5 → c_1_1·c_1_22 + c_1_12·c_1_2 + c_1_0·c_1_22 + c_1_02·c_1_2, an element of degree 3
  6. b_3_6 → c_1_0·c_1_22 + c_1_02·c_1_2, an element of degree 3
  7. b_4_7 → 0, an element of degree 4
  8. b_4_8 → 0, an element of degree 4
  9. c_4_9 → c_1_12·c_1_22 + c_1_14 + c_1_02·c_1_22 + c_1_04, an element of degree 4
  10. c_4_10 → c_1_12·c_1_22 + c_1_14, an element of degree 4
  11. b_5_16 → c_1_12·c_1_23 + c_1_14·c_1_2 + c_1_0·c_1_1·c_1_23 + c_1_0·c_1_12·c_1_22
       + c_1_02·c_1_23 + c_1_02·c_1_1·c_1_22 + c_1_02·c_1_12·c_1_2 + c_1_04·c_1_2, an element of degree 5

Restriction map to a maximal el. ab. subgp. of rank 3

  1. b_1_0 → 0, an element of degree 1
  2. b_1_1 → 0, an element of degree 1
  3. b_1_2 → c_1_2, an element of degree 1
  4. a_2_1 → 0, an element of degree 2
  5. b_3_5 → 0, an element of degree 3
  6. b_3_6 → 0, an element of degree 3
  7. b_4_7 → 0, an element of degree 4
  8. b_4_8 → c_1_1·c_1_23 + c_1_12·c_1_22, an element of degree 4
  9. c_4_9 → c_1_1·c_1_23 + c_1_14 + c_1_02·c_1_22 + c_1_04, an element of degree 4
  10. c_4_10 → c_1_12·c_1_22 + c_1_14, an element of degree 4
  11. b_5_16 → c_1_12·c_1_23 + c_1_14·c_1_2, an element of degree 5

Restriction map to a maximal el. ab. subgp. of rank 3

  1. b_1_0 → 0, an element of degree 1
  2. b_1_1 → c_1_2, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. a_2_1 → 0, an element of degree 2
  5. b_3_5 → 0, an element of degree 3
  6. b_3_6 → 0, an element of degree 3
  7. b_4_7 → c_1_1·c_1_23 + c_1_12·c_1_22 + c_1_0·c_1_23 + c_1_02·c_1_22, an element of degree 4
  8. b_4_8 → c_1_24 + c_1_1·c_1_23 + c_1_12·c_1_22 + c_1_0·c_1_23 + c_1_02·c_1_22, an element of degree 4
  9. c_4_9 → c_1_1·c_1_23 + c_1_14 + c_1_0·c_1_23 + c_1_04, an element of degree 4
  10. c_4_10 → c_1_12·c_1_22 + c_1_14, an element of degree 4
  11. b_5_16 → c_1_1·c_1_24 + c_1_12·c_1_23 + c_1_0·c_1_24 + c_1_02·c_1_23, an element of degree 5

About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 128


Simon A. King David J. Green
Fakultät für Mathematik und Informatik Fakultät für Mathematik und Informatik
Friedrich-Schiller-Universität Jena Friedrich-Schiller-Universität Jena
Ernst-Abbe-Platz 2 Ernst-Abbe-Platz 2
D-07743 Jena D-07743 Jena
Germany Germany
E-mail: simon dot king at uni hyphen jena dot de
Tel: +49 (0)3641 9-46184
Fax: +49 (0)3641 9-46162
Office: Zi. 3524, Ernst-Abbe-Platz 2
E-mail: david dot green at uni hyphen jena dot de
Tel: +49 3641 9-46166
Fax: +49 3641 9-46162
Office: Zi 3512, Ernst-Abbe-Platz 2

Last change: 25.08.2009