Yet another question:  see no reason why unbounded polyhedra are not
handled by mink_sum()

def mink_sum(polyhedra_list, verbose = False):
    """
    Returns the Minkowski sum of a list of polyhedra.
    TODO: currently only works for polytopes, not unbounded polyhedra
    """

Currently, the vertices of the sum are computed this way:

    answer = Polyhedron()
    temp_vertex_list = []
    for vertex1 in polyhedra_list[0].vertices():
        for vertex2 in polyhedra_list[1].vertices():
            temp_vertex_list.append([vertex1[i]+vertex2[i] for i in
range(len(vertex1))])
    answer._vertices = temp_vertex_list
    answer._remove_redundant_vertices()

adding

answer._rays.append(polyhedra_list[0].rays())
answer._rays.append(polyhedra_list[1].rays())

should be correct. a call to _remove_redundant_rays_and_vertices()
should be called after, I'll see if cdd has this functionality.
-- 
Sébastien Barthélemy

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