On the non-split extension group $2^{6}{^{cdot}}Sp(6,2)$

In this paper we first construct the non-split extension $overline{G}= 2^{6} {^{cdot}}Sp(6,2)$ as a permutation group acting on 128 points. We then determine the conjugacy classes using the coset analysis technique, inertia factor groups and Fischer matrices, which are required for the computations of the character table of $overline{G}$ by means of Clifford-Fischer Theory. There are two inertia factor groups namely $H_{1} = Sp(6,2)$ and $H_{2} = 2^{5}{:}S_{6},$ the Schur multiplier and hence the character table of the corresponding covering group of $H_{2}$ were calculated. Using information onconjugacy classes, Fischer matrices and ordinary and projective tables of $H_{2},$ we concluded that we only need to use the ordinary character table of $H_{2}$ to construct the character table of $overline{G}.$ The Fischer matrices of $overline{G}$ are all listed in this paper. The character table of $overline{G}$ is a $67 times 67$ integral matrix, it has been supplied in the PhD Thesis of the first author, which could be accessed online.