euler(Flat)

Synopsis

• Function: euler

• Usage:

  euler(F) or euler(A)

• Inputs:
  • F, an intersection of hyperplane(s), a flat
• Outputs:
  • k, an integer, the beta invariant of the flat F or arrangement A

Description

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