# factorization into `$XX^{T}$` may not be unique!
raise ValueError('Unable to determine extremity of ``A``.')
-
-
-def completely_positive_operators_gens(K):
- r"""
- Return a list of generators (matrices) for the completely-positive
- cone of ``K``.
-
- INPUT:
-
- - ``K`` -- a closed convex rational polyhedral cone.
-
- OUTPUT:
-
- A list of matrices, the conic hull of which is the
- completely-positive cone of ``K``.
-
- SETUP::
-
- sage: from mjo.cone.completely_positive import (
- ....: completely_positive_operators_gens,
- ....: is_completely_positive )
- sage: from mjo.cone.nonnegative_orthant import nonnegative_orthant
- sage: from mjo.matrix_vector import isomorphism
-
- EXAMPLES::
-
- sage: K = nonnegative_orthant(2)
- sage: completely_positive_operators_gens(K)
- [
- [1 0] [0 0]
- [0 0], [0 1]
- ]
- sage: all( is_completely_positive(M)
- ....: for M in completely_positive_operators_gens(K) )
- True
-
- TESTS:
-
- The completely-positive cone of ``K`` is subdual::
-
- sage: K = random_cone(max_ambient_dim=8, max_rays=10)
- sage: cp_gens = completely_positive_operators_gens(K)
- sage: n = K.lattice_dim()
- sage: M = MatrixSpace(QQ, n, n)
- sage: (p, p_inv) = isomorphism(M)
- sage: L = ToricLattice(n**2)
- sage: cp_cone = Cone( (p(m) for m in cp_gens), lattice=L )
- sage: copos_cone = Cone(cp_cone.dual().rays(), lattice=L )
- sage: all( x in copos_cone for x in cp_cone )
- True
-
- """
- return [ x.tensor_product(x) for x in K ]
-