Cohomology of group number 1833 of order 128

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General information on the group

  • The group has 4 minimal generators and exponent 8.
  • It is non-abelian.
  • It has p-Rank 4.
  • Its center has rank 2.
  • It has a unique conjugacy class of maximal elementary abelian subgroups, which is of rank 4.

Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 4 and depth 2.
  • The depth coincides with the Duflot bound.
  • The Poincaré series is
    t4  +  1
    (t  −  1)4 · (t2  +  1)2
  • The a-invariants are -∞,-∞,-4,-4,-4. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 10 minimal generators of maximal degree 5:

  1. a_1_0, a nilpotent element of degree 1
  2. a_1_3, a nilpotent element of degree 1
  3. b_1_1, an element of degree 1
  4. b_1_2, an element of degree 1
  5. b_3_10, an element of degree 3
  6. b_3_11, an element of degree 3
  7. b_4_16, an element of degree 4
  8. c_4_17, a Duflot regular element of degree 4
  9. c_4_18, a Duflot regular element of degree 4
  10. b_5_31, an element of degree 5

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Ring relations

There are 19 minimal relations of maximal degree 10:

  1. a_1_0·b_1_1 + a_1_32
  2. a_1_0·b_1_2
  3. a_1_03
  4. a_1_32·b_1_1 + a_1_0·a_1_32
  5. a_1_0·b_3_10
  6. a_1_0·b_3_11
  7. b_1_1·b_1_2·b_3_10 + b_1_12·b_3_10 + b_4_16·b_1_2
  8. b_4_16·a_1_0
  9. b_3_112 + b_1_12·b_1_2·b_3_11 + c_4_17·b_1_22
  10. b_3_102 + c_4_18·b_1_22
  11. b_3_112 + b_3_10·b_3_11 + b_1_2·b_5_31 + b_1_13·b_3_10
  12. a_1_0·b_5_31
  13. b_4_16·b_3_10 + c_4_18·b_1_1·b_1_22 + c_4_18·b_1_12·b_1_2
  14. b_1_1·b_1_2·b_5_31 + b_1_12·b_5_31 + b_1_13·b_1_2·b_3_11 + b_1_14·b_3_11
       + b_4_16·b_3_11 + b_4_16·b_1_13 + c_4_17·b_1_1·b_1_22 + c_4_17·b_1_12·b_1_2
  15. b_4_162 + c_4_18·b_1_12·b_1_22 + c_4_18·b_1_14
  16. b_3_10·b_5_31 + b_1_13·b_5_31 + b_1_15·b_3_11 + b_1_15·b_3_10 + b_4_16·b_1_1·b_3_11
       + b_4_16·b_1_14 + c_4_18·b_1_2·b_3_11 + c_4_18·b_1_13·b_1_2 + c_4_17·b_1_2·b_3_10
       + c_4_17·b_1_13·b_1_2
  17. b_3_11·b_5_31 + b_1_14·b_1_2·b_3_11 + b_4_16·b_1_1·b_3_11 + c_4_17·b_1_2·b_3_11
       + c_4_17·b_1_2·b_3_10 + c_4_17·b_1_12·b_1_22
  18. b_4_16·b_5_31 + b_4_16·b_1_12·b_3_11 + c_4_18·b_1_1·b_1_2·b_3_11
       + c_4_18·b_1_12·b_3_11 + c_4_18·b_1_14·b_1_2 + c_4_18·b_1_15 + b_4_16·c_4_17·b_1_2
  19. b_5_312 + b_1_16·b_1_2·b_3_11 + c_4_18·b_1_12·b_1_2·b_3_11 + c_4_18·b_1_16
       + c_4_17·b_1_14·b_1_22 + c_4_17·c_4_18·b_1_22 + c_4_172·b_1_22

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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_17, a Duflot regular element of degree 4
    2. c_4_18, a Duflot regular element of degree 4
    3. b_1_22 + b_1_1·b_1_2 + b_1_12, an element of degree 2
    4. b_1_22, an element of degree 2
  • The Raw Filter Degree Type of that HSOP is [-1, -1, 4, 6, 8].
  • The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -4].

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Restriction maps

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

  1. a_1_0 → 0, an element of degree 1
  2. a_1_3 → 0, an element of degree 1
  3. b_1_1 → 0, an element of degree 1
  4. b_1_2 → 0, an element of degree 1
  5. b_3_10 → 0, an element of degree 3
  6. b_3_11 → 0, an element of degree 3
  7. b_4_16 → 0, an element of degree 4
  8. c_4_17 → c_1_04, an element of degree 4
  9. c_4_18 → c_1_14, an element of degree 4
  10. b_5_31 → 0, an element of degree 5

Restriction map to a maximal el. ab. subgp. of rank 4

  1. a_1_0 → 0, an element of degree 1
  2. a_1_3 → 0, an element of degree 1
  3. b_1_1 → c_1_2, an element of degree 1
  4. b_1_2 → c_1_3, an element of degree 1
  5. b_3_10 → c_1_1·c_1_32 + c_1_12·c_1_3, an element of degree 3
  6. b_3_11 → c_1_02·c_1_3, an element of degree 3
  7. b_4_16 → c_1_1·c_1_2·c_1_32 + c_1_1·c_1_22·c_1_3 + c_1_12·c_1_2·c_1_3 + c_1_12·c_1_22, an element of degree 4
  8. c_4_17 → c_1_02·c_1_22 + c_1_04, an element of degree 4
  9. c_4_18 → c_1_12·c_1_32 + c_1_14, an element of degree 4
  10. b_5_31 → c_1_1·c_1_23·c_1_3 + c_1_12·c_1_23 + c_1_02·c_1_1·c_1_32
       + c_1_02·c_1_12·c_1_3 + c_1_04·c_1_3, an element of degree 5

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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