flat(Arrangement,List) -- make a flat from a list of indices

• Function: flat

• Usage:

  flat(A,L)

• Inputs:
  • A, a hyperplane arrangement, hyperplane arrangement
  • L, a list, list of indices in flat
• Optional inputs:
  • Validate => a Boolean value, default value true, whether or not to check if $L$ is indeed a flat of $A$ (default true)
• Outputs:
  • a flat in an hyperplane arrangement, corresponding flat

i1 : A = typeA 2

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

o1 : Hyperplane Arrangement 

i2 : flat(A, {0,1,2})

o2 = {0, 1, 2}

o2 : Flat of {x  - x , x  - x , x  - x }
               1    2   1    3   2    3