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HyperplaneArrangements :: euler(Flat)

euler(Flat)

Synopsis

Description

The beta invariant of an arrangement A is, by definition, the Euler characteristic of complement of A in complex projective space.

The beta invariant of a flat F is the beta invariant of the restriction of A to F.

i1 : A = typeA(3)

o1 = {x  - x , x  - x , x  - x , x  - x , x  - x , x  - x }
       1    2   1    3   1    4   2    3   2    4   3    4

o1 : Hyperplane Arrangement 
i2 : euler A -- for a real arrangement, equals number of bounded chambers

o2 = 2