4 ,
3 ,
1 ,
1
The Hecke algebra for the Symmetric Group
on 9 Letters, with the Partition
[ 4, 3, 1, 1 ]
in characteristic 2
.
The Module M
The module M is the permutation module over the prime
field of chacteristic 2, having point stablilizer
equal to the Young subgroup of the partition.
The dimension of M is 2520
.
The dimensions of the irreducible submodules modules are
160,
78,
48,
40,
26,
16,
8,
1
.
The module M has radical filtration (Loewy series)
2,
2,
3,
3,
3,
3,
5,
5,
5,
7,
7,
7,
8
1,
3,
5,
6,
6,
6,
7,
8,
8,
8,
8
1,
2,
2,
4,
5,
5,
5,
5,
7,
8,
8,
8,
8
3,
4,
4,
4,
5,
5,
5,
6,
7,
8,
8
2,
5,
6,
6,
6,
8,
8,
8,
8,
8,
8
2,
2,
2,
5,
8,
8,
8,
8,
8,
8,
8
4,
4,
4,
5,
5,
5,
5,
5,
5
6,
6,
6,
8,
8,
8,
8
2,
5,
8,
8
5,
5,
8
4
8
2
The module M has socle filtration (socle series)
2
8
4
5,
5,
8
2,
5,
8,
8
6,
6,
6,
8,
8,
8,
8
4,
4,
4,
5,
5,
5,
5,
5,
5
2,
2,
2,
5,
8,
8,
8,
8,
8,
8,
8
2,
5,
6,
6,
6,
8,
8,
8,
8,
8,
8
3,
4,
4,
4,
5,
5,
5,
6,
7,
8,
8
1,
2,
2,
4,
5,
5,
5,
5,
7,
8,
8,
8,
8
1,
3,
5,
6,
6,
6,
7,
8,
8,
8,
8
2,
2,
3,
3,
3,
3,
5,
5,
5,
7,
7,
7,
8
The module M has simple direct summands:
2 copies of simple module number 3
2 copies of simple module number 7
The remaining indecomposable components of M
have radical and socle filtrations as follows:
1).
radical layers
8
5
8
8
5
8
socle layers
8
5
8
8
5
8
2).
radical layers
3,
3,
7
1,
3,
7
1,
7
3,
7
socle layers
3,
7
1,
7
1,
3,
7
3,
3,
7
3).
radical layers
2,
5
6,
8
5,
8
4,
5
6,
8
2,
8
5
socle layers
5
2,
8
6,
8
4,
5
5,
8
6,
8
2,
5
4).
radical layers
5
6,
8
2,
5,
8
4,
5
6,
8,
8
2,
8,
8
4,
5,
5
6,
8
8
5
socle layers
5
8
6,
8
4,
5,
5
2,
8,
8
6,
8,
8
4,
5
2,
5,
8
6,
8
5
5).
radical layers
5
6,
8
2,
5,
8
4,
5
6,
8,
8
2,
8,
8
4,
5,
5
6,
8
8
5
socle layers
5
8
6,
8
4,
5,
5
2,
8,
8
6,
8,
8
4,
5
2,
5,
8
6,
8
5
6).
radical layers
2
8
4,
5
6,
8
2,
8
5,
8
4,
5
6,
8,
8
2,
5
8
4
8
2
socle layers
2
8
4
8
2,
5
6,
8,
8
4,
5
5,
8
2,
8
6,
8
4,
5
8
2
The Action Algebra
The action algebra A is the image of kG in the
k-endomorphism ring of M. It's simple modules are the irreducible
submodules of M.
The dimensions of the projective modules are
384,
576,
320,
555,
826,
477,
448,
1488
.
The cartan matrix of A is
2,
0,
1,
0,
0,
0,
2,
0
0,
4,
0,
3,
4,
2,
0,
8
1,
0,
3,
0,
0,
0,
2,
0
0,
3,
0,
4,
4,
3,
0,
9
0,
4,
0,
4,
10,
5,
0,
14
0,
2,
0,
3,
5,
4,
0,
7
2,
0,
2,
0,
0,
0,
4,
0
0,
8,
0,
9,
14,
7,
0,
28
The determinant of the Cartan matrix is 432.
The blocks of A consist of the following irreducible
modules:
(1).
1,
3,
7
(2).
2,
4,
5,
6,
8
The radical and socle filtrations of the projective
modules for A are the following:
Projective module number 1
radical layers
1
1,
7
3,
7
socle layers
1
1,
7
3,
7
Projective module number 2
radical layers
2
8
4,
5
6,
8
2,
8
5,
8
4,
5
6,
8,
8
2,
5
8
4
8
2
socle layers
2
8
4
8
2,
5
6,
8,
8
4,
5
5,
8
2,
8
6,
8
4,
5
8
2
Projective module number 3
radical layers
3
3,
3,
7
1
7
socle layers
3
7
1
3,
3,
7
Projective module number 4
radical layers
4
6,
8
2,
4,
8
5,
6,
8
4,
5,
8
6,
8,
8,
8
2,
5,
5
8
4
8
2
socle layers
4
8
2
6,
8,
8
4,
5
5,
8
2,
8
4,
6,
8
4,
5,
8
6,
8,
8
2,
5
Projective module number 5
radical layers
5
5,
6,
8
2,
5,
6,
8,
8
4,
5,
5,
5,
8
4,
6,
6,
8,
8,
8
2,
5,
8,
8,
8,
8
2,
4,
4,
5,
5
6,
8,
8
2,
8
5
socle layers
5
8
6,
8
4,
5,
5
2,
5,
5,
8,
8
6,
8,
8,
8,
8
4,
5,
6,
6,
8,
8
2,
4,
4,
5,
5,
5,
8
6,
8,
8,
8
2,
2,
5
Projective module number 6
radical layers
6
4,
5
5,
6,
8
2,
4,
6,
8,
8
5,
5,
6,
8
4,
8
8,
8
2,
5
socle layers
6
4,
5
5,
8
6,
8,
8
4,
5,
6,
8
2,
4,
5,
8
6,
8,
8
2,
5
Projective module number 7
radical layers
7
1,
3,
7
1,
7
3,
7
socle layers
7
1,
7
1,
7
3,
3,
7
Projective module number 8
radical layers
8
2,
4,
5,
8
4,
5,
5,
6,
8,
8,
8
2,
4,
5,
6,
6,
8,
8,
8,
8,
8
2,
4,
5,
5,
5,
6,
8,
8,
8,
8,
8,
8
2,
4,
4,
4,
5,
5,
5,
5,
6,
8,
8
6,
6,
8,
8,
8,
8,
8,
8
2,
2,
4,
5,
5,
8
5,
8,
8
2,
4
8
2
socle layers
8
4
8
2,
2,
5
6,
8,
8,
8,
8
4,
4,
4,
5,
5
5,
5,
5,
8,
8,
8,
8,
8
2,
2,
6,
8,
8,
8,
8,
8,
8
4,
4,
5,
6,
6,
6,
8,
8,
8
2,
4,
4,
4,
5,
5,
5,
5,
5,
8,
8
6,
6,
8,
8,
8,
8,
8
2,
2,
2,
5,
5,
8
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1,
1
.
The Hecke Algebra
The Hecke algebra H of the module M is the A-endomorphism
ring of M.
The dimension of H is
101
.
The dimensions of the irreducible H-modules are
2,
2,
2,
1,
1,
1,
1
.
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1
.
The dimensions of the projective modules of H are
4,
3,
20,
8,
14,
15,
10
.
The cartan matrix of H is
1,
0,
0,
0,
2,
0,
0
0,
1,
0,
0,
1,
0,
0
0,
0,
6,
2,
0,
4,
2
0,
0,
2,
3,
0,
1,
0
2,
1,
0,
0,
8,
0,
0
0,
0,
4,
1,
0,
4,
2
0,
0,
2,
0,
0,
2,
4
The determinant of the Cartan matrix is 156.
The blocks of H consist of the following irreducible
modules:
(1).
1,
2,
5
(2).
3,
4,
6,
7
The radical and socle filtrations of the projective
modules for H are the following:
Projective module number 1
radical layers
1
5
5
socle layers
1
5
5
Projective module number 2
radical layers
2
5
socle layers
2
5
Projective module number 3
radical layers
3
3,
4,
6
3,
6,
7
3,
4,
6,
7
3,
6
3
socle layers
3
3,
6
3,
4,
6
3,
6
3,
4,
6
3,
7,
7
Projective module number 4
radical layers
4
3,
4,
4
6
3
socle layers
4
3
4,
6
3,
4
Projective module number 5
radical layers
5
1,
2,
5,
5
1,
5,
5
5,
5
5
socle layers
5
5
1,
1
2,
5,
5,
5
5,
5,
5
Projective module number 6
radical layers
6
3,
6,
7
3,
4,
6
3,
6
3,
7
socle layers
6
3
3,
6
3,
4,
6,
6,
7
3,
7
Projective module number 7
radical layers
7
6,
7
3,
7
3
6
7
socle layers
7
6
3
3,
7
6,
7
7
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