arXiv subjects

Gerhard O. Michler

Publications and source records attributed to Gerhard O. Michler.

3 recordsLinked to original sources

arXiv2009

Construction of Co_1 from an irreducible subgroup M_{24} of GL_{11}(2)

In this article we give an self contained existence proof for J. Conway's sporadic simple group Co_1 [4] using the second author's algorithm [14] constructing finite simple groups from irreducible subgroups of GL_n(2). Here n = 11 and the irreducible subgroup is the Mathieu group M_{24}. From the split extension E of M_{24} by a uniquely determined 11-dimensional GF(2)M_{24}-module V we construct the centralizer H = C_G(z) of a 2-central involution z of E in an unknown target group G. Then we prove that all the conditions of Algorithm 2.5 of [14] are satisfied. This allows us to construct a simple subgroup G of GL_{276}(23) which we prove to be isomorphic with Conway's original sporadic simple group Co_1 by means of a constructed faithful permutation representation of G and Soicher's presentation [16] of the original Conway group Co_1.

math.GR↗

arXiv2009

Construction of Fischer's sporadic group Fi'_{24} inside GL_{8671}(13)

In this article we construct an irreducible simple subgroup G = of GL_{8671}(13) from an irreducible subgroup T of GL_{11}(2) isomorphic to Mathieu's simple group M_{24} by means of Algorithm 2.5 of [13]. We also use the first author's similar construction of Fischer's sporadic simple group G_1 = Fi_{23} described in [11]. He starts from an irreducible subgroup T_1 of GL_{11}(2) contained in T which is isomorphic to M_{23}. In [7] J. Hall and L. S. Soicher published a nice presentation of Fischer's original 3-transposition group Fi_{24} [6]. It is used here to show that G is isomorphic to the simple commutator subgroup Fi'_{24} of Fi_{24}. We also determine a faithful permutation representation of G of degree 306936 with stabilizer G_1 = $\cong$ Fi_{23}. It enabled MAGMA to calculate the character table of G automatically. Furthermore, we prove that G has two conjugacy classes of involutions z and u such that C_G(u) = $\cong$ 2Aut(\Fi_{22}). Moreover, we determine a presentation of H = C_G(z) and a faithful permutation representation of degree 258048 for which we document a stabilizer.

math.GR↗

arXiv2009

Simultaneous Constructions of the Sporadic Groups Co_2 and Fi_{22}

In this article we give self-contained existence proofs for the sporadic simple groups Co_2 and Fi_{22} using the second author's algorithm [10] constructing finite simple groups from irreducible subgroups of GL_n(2). These two sporadic groups were originally discovered by J. Conway [4] and B. Fischer [7], respectively, by means of completely different and unrelated methods. In this article n=10 and the irreducible subgroups are the Mathieu group M_{22} and its automorphism group Aut(M_{22}). We construct their five non-isomorphic extensions E_i by the two 10-dimensional non-isomorphic simple modules of M_{22} and by the two 10-dimensional simple modules of A_{22} = Aut(M_{22}) over F=GF(2). In two cases we construct the centralizer H_i = C_{G_i}(z_i) of a 2-central involution z_i of E_i in any target simple group G_i. Then we prove that all the conditions of Algorithm 7.4.8 of [11] are satisfied. This allows us to construct G_3 $\cong$ Co_2 inside GL_{23}(13) and G_2 $\cong$ Fi_{22} inside GL_{78}(13). We also calculate their character tables and presentations.

math.GR↗