GROUP OF ORDER 16 #11

GROUP #11

The MAGMA library number for G is 6

GrpPC : G of order 16 = 2^4 PC-Relations: G.1^2 = G.3, G.3^2 = G.4, G.2^G.1 = G.2 * G.4

The center of G is abelian of type [ 4 ] .
The orders of the terms of the lower central series are [ 16, 2, 1 ] .
The orders of the terms of the upper central series are [ 1, 4, 16 ] .
The order of the Frattini subgroup is 4.
The exponent of G is 8.
G has a unique maximal elementary abelian subgroup which is normal and has order 4. Its centralizer has order 8.

The cohomology ring of G is the quotient of a polynomial ring in the variables
[ z, y, x, w ] in degrees [ 1, 1, 3, 4 ] , by the ideal generated by the relations
z2 ,
zy2 ,
zx ,
x2 .

The Hilbert series for the cohomology ring is
1 / t4 -2t3+ 2t2 -2t+ 1.
Its denominator factors as ( t-1 )2 ( t2+1 ) .

The Krull dimension of the cohomology ring is 2.
The longest regular sequence consists of the generators w .
A homogeneous set of parameters is the set w , y2 of degrees [ 4, 2 ] .

The hypercohomolgy spectral sequence has E2 term:

ROW (1) : [] [ z ] [ zy ]
ROW (0) : [1] [ y, z ] [ zy ] [ x ] [ yx ]

Restriction to the Maximal Elementary Abelian Subgroup

Generated by [ G.4, G.2 * G.4 ] The cohomology ring of E is a polynomial ring in the variables z , y .

The images of the generators of the cohomology of G restricted to E are
0 ,
z ,
0 ,
z2y2 + y4
in the cohomology of E.

The kernel of the restriction to E (Minimal Prime) of the cohomology of G is generated by
z ,
x .

This ideal is also the nilradical of the cohomology of G.

It is nilpotent of degree 2.

Restrictions to Maximal Subgroups

Maximal Subgroup H #1

The group H is abelian of type [ 8 ]

The cohomology ring of H is a the quotient of a polynomial ring in the variables
[ z, y ] , in degrees [ 1, 2 ] , by the ideal of relations
z2 .

The images of the generators of the cohomology of G restricted to H are
z ,
z ,
zy ,
y2
in the cohomology of H.

The kernel of the restriction to H of the cohomology of G is generated by
z + y .

Maximal Subgroup H #2

The group H is abelian of type [ 4, 2 ]

The cohomology ring of H is a the quotient of a polynomial ring in the variables
[ z, y, x ] , in degrees [ 1, 1, 2 ] , by the ideal of relations
z2 .

The images of the generators of the cohomology of G restricted to H are
0 ,
y ,
zy2 ,
y2x + x2
in the cohomology of H.

The kernel of the restriction to H of the cohomology of G is generated by
z .

Maximal Subgroup H #3

The group H is abelian of type [ 8 ]

The cohomology ring of H is a the quotient of a polynomial ring in the variables
[ z, y ] , in degrees [ 1, 2 ] , by the ideal of relations
z2 .

The images of the generators of the cohomology of G restricted to H are
z ,
0 ,
zy ,
y2
in the cohomology of H.

The kernel of the restriction to H of the cohomology of G is generated by
y .

The essential cohomology of G is generated as an ideal by
zy .

It is nilpotent of degree 2.
The annihilator of the Essential Cohomology has dimension 1 .
The essential cohomology is a free module over the polynomial subring Q of the cohomology ring of G generated by w
The essential cohomology is generated as a module over Q by the elements
[] [ zy ]

Inflations from Maximal Quotient Groups

Maximal Quotient Group Q #1

The kernel of the quotient is generated by G.4 .

The group Q is abelian of type [ 4, 2 ] .

The cohomology ring of Q is a the quotient of a polynomial ring in the variables
[ z, y, x ] , in degrees [ 1, 1, 2 ] , by the ideal of relations
z2 .

The images of the generators of the cohomology of Q inflated to G are
z ,
y ,
zy + y2
in the cohomology of G.

The kernel of the inflation to G of the cohomology of Q is generated by
zy + y2 + x ,
zx .

Action of Automorphisms

The groups of outer automorphisms of G has order 4, and is generated by 2 elements.

Automorphism #1

The order of the class of the automorphism in the outer automorphism group is 2. The images of the generators of G are

    G.1 * G.3
    G.2
    G.3 * G.4
    G.4 .

The images of the generators of the cohomology of G under the map induced by the automorphism are
z ,
y ,
x ,
w .

Automorphism #2

The order of the class of the automorphism in the outer automorphism group is 2. The images of the generators of G are

    G.1 * G.2
    G.2
    G.3 * G.4
    G.4 .

The images of the generators of the cohomology of G under the map induced by the automorphism are
z ,
z + y ,
x ,
w .

CHECKS

paramflag = true
qregflagflag = true
cmflag = false
essflag = true
centflag = true

THE COMPUTATION IS COMPLETE