- if K2 is None:
- K2 = K
-
- # First we project K onto the span of K2. This will explode if the
- # rank of ``K2.lattice()`` doesn't match ours.
- span_K2 = Cone(K2.rays() + (-K2).rays(), lattice=K.lattice())
- K = K.intersection(span_K2)
-
- # Cheat a little to get the subspace span(K2). The paper uses the
- # rays of K2 as a basis, but everything is invariant under linear
- # isomorphism (i.e. a change of basis), and this is a little
- # faster.
- W = span_K2.linear_subspace()
+ # First we want to intersect ``K`` with ``W``. The easiest way to
+ # do this is via cone intersection, so we turn the subspace ``W``
+ # into a cone.
+ W_cone = Cone(W.basis() + [-b for b in W.basis()], lattice=K.lattice())
+ K = K.intersection(W_cone)