Cohomology of group number 2179 of order 128

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General information on the group

  • The group has 5 minimal generators and exponent 4.
  • It is non-abelian.
  • It has p-Rank 4.
  • Its center has rank 3.
  • It has 3 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 4.

Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 4 and depth 3.
  • The depth coincides with the Duflot bound.
  • The Poincaré series is
    t6  +  t5  +  t2  +  t  +  1
    (t  −  1)4 · (t2  +  1) · (t4  +  1)
  • The a-invariants are -∞,-∞,-∞,-6,-4. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 9 minimal generators of maximal degree 8:

  1. a_1_2, a nilpotent element of degree 1
  2. b_1_0, an element of degree 1
  3. b_1_1, an element of degree 1
  4. b_1_3, an element of degree 1
  5. c_1_4, a Duflot regular element of degree 1
  6. c_2_13, a Duflot regular element of degree 2
  7. b_5_76, an element of degree 5
  8. b_5_77, an element of degree 5
  9. c_8_219, a Duflot regular element of degree 8

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Ring relations

There are 10 minimal relations of maximal degree 10:

  1. a_1_2·b_1_0
  2. b_1_12 + b_1_0·b_1_3 + b_1_0·b_1_1 + a_1_2·b_1_1 + a_1_22
  3. b_1_0·b_1_32 + a_1_23
  4. a_1_23·b_1_32
  5. a_1_2·b_5_76 + c_2_13·a_1_2·b_1_33 + c_2_13·a_1_2·b_1_1·b_1_32
       + c_2_13·a_1_22·b_1_1·b_1_3 + c_2_13·a_1_23·b_1_3 + c_2_132·a_1_22
  6. b_1_0·b_5_77 + c_2_13·a_1_23·b_1_1 + c_2_132·b_1_0·b_1_3
  7. b_1_32·b_5_76 + a_1_22·b_5_77 + c_2_13·b_1_35 + c_2_13·b_1_1·b_1_34
       + c_2_13·a_1_2·b_1_1·b_1_33 + c_2_13·a_1_22·b_1_33
       + c_2_13·a_1_22·b_1_1·b_1_32 + c_2_132·a_1_2·b_1_32 + c_2_132·a_1_22·b_1_3
       + c_2_132·a_1_23
  8. b_5_76·b_5_77 + c_2_13·b_1_33·b_5_77 + c_2_13·b_1_1·b_1_32·b_5_77
       + c_2_13·a_1_2·b_1_1·b_1_3·b_5_77 + c_2_13·a_1_22·b_1_3·b_5_77
       + c_2_13·a_1_22·b_1_36 + c_2_13·a_1_22·b_1_1·b_5_77 + c_2_132·b_1_3·b_5_76
       + c_2_132·a_1_2·b_5_77 + c_2_133·b_1_34 + c_2_133·b_1_1·b_1_33
       + c_2_133·a_1_2·b_1_1·b_1_32 + c_2_133·a_1_22·b_1_32
       + c_2_133·a_1_22·b_1_1·b_1_3 + c_2_133·a_1_23·b_1_1 + c_2_134·a_1_2·b_1_3
  9. b_5_762 + b_1_03·b_1_1·b_1_3·b_5_76 + b_1_04·b_1_3·b_5_76 + b_1_08·b_1_1·b_1_3
       + b_1_09·b_1_1 + c_8_219·b_1_02 + c_2_13·b_1_02·b_1_1·b_5_76
       + c_2_13·b_1_03·b_5_76 + c_2_13·b_1_06·b_1_1·b_1_3 + c_2_13·b_1_07·b_1_3
       + c_2_132·b_1_36 + c_2_132·b_1_04·b_1_1·b_1_3 + c_2_132·b_1_05·b_1_3
       + c_2_132·a_1_2·b_1_1·b_1_34 + c_2_132·a_1_22·b_1_34 + c_2_133·b_1_03·b_1_1
       + c_2_134·a_1_22
  10. b_5_772 + a_1_2·b_1_34·b_5_77 + a_1_22·b_1_1·b_1_32·b_5_77 + c_2_13·b_1_38
       + c_2_13·a_1_2·b_1_1·b_1_36 + c_8_219·a_1_22 + c_2_13·a_1_22·b_1_1·b_5_77
       + c_2_132·a_1_2·b_1_35 + c_2_132·a_1_2·b_1_1·b_1_34 + c_2_132·a_1_22·b_1_34
       + c_2_133·a_1_22·b_1_32 + c_2_133·a_1_22·b_1_1·b_1_3 + c_2_134·b_1_32
       + c_2_134·a_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_1_4, a Duflot regular element of degree 1
    2. c_2_13, a Duflot regular element of degree 2
    3. c_8_219, a Duflot regular element of degree 8
    4. b_1_32 + b_1_02, an element of degree 2
  • The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 5, 9].
  • 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 3

  1. a_1_2 → 0, an element of degree 1
  2. b_1_0 → 0, an element of degree 1
  3. b_1_1 → 0, an element of degree 1
  4. b_1_3 → 0, an element of degree 1
  5. c_1_4 → c_1_0, an element of degree 1
  6. c_2_13 → c_1_22, an element of degree 2
  7. b_5_76 → 0, an element of degree 5
  8. b_5_77 → 0, an element of degree 5
  9. c_8_219 → c_1_18, an element of degree 8

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

  1. a_1_2 → 0, an element of degree 1
  2. b_1_0 → c_1_3, an element of degree 1
  3. b_1_1 → 0, an element of degree 1
  4. b_1_3 → 0, an element of degree 1
  5. c_1_4 → c_1_0, an element of degree 1
  6. c_2_13 → c_1_2·c_1_3 + c_1_22, an element of degree 2
  7. b_5_76 → c_1_12·c_1_33 + c_1_14·c_1_3, an element of degree 5
  8. b_5_77 → 0, an element of degree 5
  9. c_8_219 → c_1_12·c_1_2·c_1_35 + c_1_12·c_1_22·c_1_34 + c_1_14·c_1_34
       + c_1_14·c_1_2·c_1_33 + c_1_14·c_1_22·c_1_32 + c_1_18, an element of degree 8

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

  1. a_1_2 → 0, an element of degree 1
  2. b_1_0 → 0, an element of degree 1
  3. b_1_1 → 0, an element of degree 1
  4. b_1_3 → c_1_3, an element of degree 1
  5. c_1_4 → c_1_0, an element of degree 1
  6. c_2_13 → c_1_22, an element of degree 2
  7. b_5_76 → c_1_22·c_1_33, an element of degree 5
  8. b_5_77 → c_1_2·c_1_34 + c_1_24·c_1_3, an element of degree 5
  9. c_8_219 → c_1_22·c_1_36 + c_1_26·c_1_32 + c_1_14·c_1_34 + c_1_18, an element of degree 8

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

  1. a_1_2 → 0, an element of degree 1
  2. b_1_0 → c_1_3, an element of degree 1
  3. b_1_1 → c_1_3, an element of degree 1
  4. b_1_3 → 0, an element of degree 1
  5. c_1_4 → c_1_0, an element of degree 1
  6. c_2_13 → c_1_2·c_1_3 + c_1_22, an element of degree 2
  7. b_5_76 → c_1_35 + c_1_12·c_1_33 + c_1_14·c_1_3, an element of degree 5
  8. b_5_77 → 0, an element of degree 5
  9. c_8_219 → c_1_23·c_1_35 + c_1_24·c_1_34 + c_1_25·c_1_33 + c_1_26·c_1_32
       + c_1_14·c_1_34 + c_1_18, an element of degree 8

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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