contraction -- contraction of subset of matroid

• Usage:

  contraction(M, S)

  M / S

• Inputs:
  • M, a matroid,
  • S, a set, of indices, or a list of elements in M
• Outputs:
  • a matroid, the contraction M / S

i1 : M = matroid({a,b,c,d},{{a,b},{a,c}})

o1 = a "matroid" of rank 2 on 4 elements

o1 : Matroid

i2 : N = M / {c}

o2 = a "matroid" of rank 1 on 3 elements

o2 : Matroid

i3 : peek N

o3 = Matroid{bases => {set {0}}          }
             cache => CacheTable{...2...}
             groundSet => set {0, 1, 2}
             rank => 1

i4 : N == M / set{2}

o4 = true