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The 112 roots with integer entries form a D 8 root system. The E 8 root system also contains a copy of A 8 (which has 72 roots) as well as E 6 and E 7 (in fact, the latter two are usually defined as subsets of E 8). In the odd coordinate system, E 8 is given by taking the roots in the even coordinate system and changing the sign of any one ...
The root system E 7 is the set of vectors in E 8 that are perpendicular to a fixed root in E 8. The root system E 7 has 126 roots. The root system E 6 is not the set of vectors in E 7 that are perpendicular to a fixed root in E 7, indeed, one obtains D 6 that way. However, E 6 is the subsystem of E 8 perpendicular to two suitably chosen roots ...
The name derives from the fact that it is the root lattice of the E 8 root system. The norm [1] of the E 8 lattice (divided by 2) is a positive definite even unimodular quadratic form in 8 variables, and conversely such a quadratic form can be used to construct a positive-definite, even, unimodular lattice of rank 8.
The root lattice generated by the root system, as in the E 8 lattice. This is naturally defined, but not one-to-one – for example, A 2 and G 2 both generate the hexagonal lattice . An associated polytope – for example Gosset 4 21 polytope may be referred to as "the E 8 polytope", as its vertices are derived from the E 8 root system and it ...
For root systems, no root maps to zero, corresponding to the Coxeter element not fixing any root or rather axis (not having eigenvalue 1 or −1), so the projections of orbits under w form h-fold circular arrangements [9] and there is an empty center, as in the E 8 diagram at above right. For polytopes, a vertex may map to zero, as depicted below.
E 8, an exceptional simple Lie group with root lattice of rank 8; E 8 lattice, special lattice in R 8; E 8 manifold, mathematical object with no smooth structure or topological triangulation; E 8 polytope, alternate name for the 4 21 semiregular (uniform) polytope; Elementary abelian group of order 8
By the definition of a root system, each preserves , from which it follows that is a finite group. In the case of the A 2 {\displaystyle A_{2}} root system, for example, the hyperplanes perpendicular to the roots are just lines, and the Weyl group is the symmetry group of an equilateral triangle, as indicated in the figure.
An alternative (7-dimensional) description of the root system, which is useful in considering E 7 × SU(2) as a subgroup of E 8, is the following: All () permutations of (±1,±1,0,0,0,0,0) preserving the zero at the last entry, all of the following roots with an even number of + 1 / 2