an element of ``K1``. Moreover, any nonnegative linear combination of
these matrices shares the same property.
+ .. SEEALSO::
+
+ :meth:`cross_positive_operator_gens`, :meth:`Z_operator_gens`,
+
REFERENCES:
.. [Orlitzky-Pi-Z]
return [ M(v.list()) for v in pi_cone ]
-def Z_operator_gens(K):
+def cross_positive_operator_gens(K):
r"""
- Compute generators of the cone of Z-operators on this cone.
+ Compute generators of the cone of cross-positive operators on this
+ cone.
OUTPUT:
A list of `n`-by-``n`` matrices where ``n == K.lattice_dim()``.
Each matrix ``L`` in the list should have the property that
- ``(L*x).inner_product(s) <= 0`` whenever ``(x,s)`` is an element of
+ ``(L*x).inner_product(s) >= 0`` whenever ``(x,s)`` is an element of
this cone's :meth:`discrete_complementarity_set`. Moreover, any
conic (nonnegative linear) combination of these matrices shares the
same property.
+ .. SEEALSO::
+
+ :meth:`positive_operator_gens`, :meth:`Z_operator_gens`,
+
REFERENCES:
M. Orlitzky.
EXAMPLES:
- Z-operators on the nonnegative orthant are just Z-matrices.
- That is, matrices whose off-diagonal elements are nonnegative::
+ Cross-positive operators on the nonnegative orthant are negations
+ of Z-matrices; that is, matrices whose off-diagonal elements are
+ nonnegative::
sage: K = Cone([(1,0),(0,1)])
- sage: Z_operator_gens(K)
+ sage: cross_positive_operator_gens(K)
[
- [ 0 -1] [ 0 0] [-1 0] [1 0] [ 0 0] [0 0]
- [ 0 0], [-1 0], [ 0 0], [0 0], [ 0 -1], [0 1]
+ [0 1] [0 0] [1 0] [-1 0] [0 0] [ 0 0]
+ [0 0], [1 0], [0 0], [ 0 0], [0 1], [ 0 -1]
]
sage: K = Cone([(1,0,0,0),(0,1,0,0),(0,0,1,0),(0,0,0,1)])
- sage: all([ z[i][j] <= 0 for z in Z_operator_gens(K)
- ....: for i in range(z.nrows())
- ....: for j in range(z.ncols())
+ sage: all([ c[i][j] >= 0 for c in cross_positive_operator_gens(K)
+ ....: for i in range(c.nrows())
+ ....: for j in range(c.ncols())
....: if i != j ])
True
- The trivial cone in a trivial space has no Z-operators::
+ The trivial cone in a trivial space has no cross-positive operators::
sage: K = Cone([], ToricLattice(0))
- sage: Z_operator_gens(K)
+ sage: cross_positive_operator_gens(K)
[]
- Every operator is a Z-operator on the ambient vector space::
+ Every operator is a cross-positive operator on the ambient vector
+ space::
sage: K = Cone([(1,),(-1,)])
sage: K.is_full_space()
True
- sage: Z_operator_gens(K)
- [[-1], [1]]
+ sage: cross_positive_operator_gens(K)
+ [[1], [-1]]
sage: K = Cone([(1,0),(-1,0),(0,1),(0,-1)])
sage: K.is_full_space()
True
- sage: Z_operator_gens(K)
+ sage: cross_positive_operator_gens(K)
[
- [-1 0] [1 0] [ 0 -1] [0 1] [ 0 0] [0 0] [ 0 0] [0 0]
- [ 0 0], [0 0], [ 0 0], [0 0], [-1 0], [1 0], [ 0 -1], [0 1]
+ [1 0] [-1 0] [0 1] [ 0 -1] [0 0] [ 0 0] [0 0] [ 0 0]
+ [0 0], [ 0 0], [0 0], [ 0 0], [1 0], [-1 0], [0 1], [ 0 -1]
]
- A non-obvious application is to find the Z-operators on the
- right half-plane::
+ A non-obvious application is to find the cross-positive operators
+ on the right half-plane::
sage: K = Cone([(1,0),(0,1),(0,-1)])
- sage: Z_operator_gens(K)
+ sage: cross_positive_operator_gens(K)
[
- [-1 0] [1 0] [ 0 0] [0 0] [ 0 0] [0 0]
- [ 0 0], [0 0], [-1 0], [1 0], [ 0 -1], [0 1]
+ [1 0] [-1 0] [0 0] [ 0 0] [0 0] [ 0 0]
+ [0 0], [ 0 0], [1 0], [-1 0], [0 1], [ 0 -1]
]
- Z-operators on a subspace are Lyapunov-like and vice-versa::
+ Cross-positive operators on a subspace are Lyapunov-like and
+ vice-versa::
sage: K = Cone([(1,0),(-1,0),(0,1),(0,-1)])
sage: K.is_full_space()
True
sage: lls = span([ vector(l.list()) for l in K.lyapunov_like_basis() ])
- sage: zs = span([ vector(z.list()) for z in Z_operator_gens(K) ])
- sage: zs == lls
+ sage: cs = span([ vector(c.list()) for c in cross_positive_operator_gens(K) ])
+ sage: cs == lls
True
TESTS:
- The Z-property is possessed by every Z-operator::
+ The cross-positive property is possessed by every cross-positive
+ operator::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
- sage: Z_of_K = Z_operator_gens(K)
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
sage: dcs = K.discrete_complementarity_set()
- sage: all([(z*x).inner_product(s) <= 0 for z in Z_of_K
+ sage: all([(c*x).inner_product(s) >= 0 for c in Sigma_of_K
....: for (x,s) in dcs])
True
- The lineality space of the cone of Z-operators is the space of
- Lyapunov-like operators::
+ The lineality space of the cone of cross-positive operators is the
+ space of Lyapunov-like operators::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
sage: L = ToricLattice(K.lattice_dim()**2)
- sage: Z_cone = Cone([ z.list() for z in Z_operator_gens(K) ],
- ....: lattice=L,
- ....: check=False)
+ sage: Sigma_cone = Cone([ c.list() for c in cross_positive_operator_gens(K) ],
+ ....: lattice=L,
+ ....: check=False)
sage: ll_basis = [ vector(l.list()) for l in K.lyapunov_like_basis() ]
sage: lls = L.vector_space().span(ll_basis)
- sage: Z_cone.linear_subspace() == lls
+ sage: Sigma_cone.linear_subspace() == lls
True
- The lineality of the Z-operators on a cone is the Lyapunov
- rank of that cone::
+ The lineality of the cross-positive operators on a cone is the
+ Lyapunov rank of that cone::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
- sage: Z_of_K = Z_operator_gens(K)
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
sage: L = ToricLattice(K.lattice_dim()**2)
- sage: Z_cone = Cone([ z.list() for z in Z_of_K ],
- ....: lattice=L,
- ....: check=False)
- sage: Z_cone.lineality() == K.lyapunov_rank()
+ sage: Sigma_cone = Cone([ c.list() for c in Sigma_of_K ],
+ ....: lattice=L,
+ ....: check=False)
+ sage: Sigma_cone.lineality() == K.lyapunov_rank()
True
- The lineality spaces of the duals of the positive and Z-operator
- cones are equal. From this it follows that the dimensions of the
- Z-operator cone and positive operator cone are equal::
+ The lineality spaces of the duals of the positive and cross-positive
+ operator cones are equal. From this it follows that the dimensions of
+ the cross-positive operator cone and positive operator cone are equal::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
sage: pi_of_K = positive_operator_gens(K)
- sage: Z_of_K = Z_operator_gens(K)
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
sage: L = ToricLattice(K.lattice_dim()**2)
sage: pi_cone = Cone([p.list() for p in pi_of_K],
....: lattice=L,
....: check=False)
- sage: Z_cone = Cone([ z.list() for z in Z_of_K],
- ....: lattice=L,
- ....: check=False)
- sage: pi_cone.dim() == Z_cone.dim()
+ sage: Sigma_cone = Cone([ c.list() for c in Sigma_of_K],
+ ....: lattice=L,
+ ....: check=False)
+ sage: pi_cone.dim() == Sigma_cone.dim()
True
sage: pi_star = pi_cone.dual()
- sage: z_star = Z_cone.dual()
- sage: pi_star.linear_subspace() == z_star.linear_subspace()
+ sage: sigma_star = Sigma_cone.dual()
+ sage: pi_star.linear_subspace() == sigma_star.linear_subspace()
True
The trivial cone, full space, and half-plane all give rise to the
sage: K.is_trivial()
True
sage: L = ToricLattice(n^2)
- sage: Z_of_K = Z_operator_gens(K)
- sage: Z_cone = Cone([z.list() for z in Z_of_K],
- ....: lattice=L,
- ....: check=False)
- sage: actual = Z_cone.dim()
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
+ sage: Sigma_cone = Cone([c.list() for c in Sigma_of_K],
+ ....: lattice=L,
+ ....: check=False)
+ sage: actual = Sigma_cone.dim()
sage: actual == n^2
True
sage: K = K.dual()
sage: K.is_full_space()
True
- sage: Z_of_K = Z_operator_gens(K)
- sage: Z_cone = Cone([z.list() for z in Z_of_K],
- ....: lattice=L,
- ....: check=False)
- sage: actual = Z_cone.dim()
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
+ sage: Sigma_cone = Cone([ c.list() for c in Sigma_of_K ],
+ ....: lattice=L,
+ ....: check=False)
+ sage: actual = Sigma_cone.dim()
sage: actual == n^2
True
sage: K = Cone([(1,0),(0,1),(0,-1)])
- sage: Z_of_K = Z_operator_gens(K)
- sage: Z_cone = Cone([z.list() for z in Z_of_K], check=False)
- sage: Z_cone.dim() == 3
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
+ sage: Sigma_cone = Cone([ c.list() for c in Sigma_of_K ], check=False)
+ sage: Sigma_cone.dim() == 3
True
- The Z-operators of a permuted cone can be obtained by conjugation::
+ The cross-positive operators of a permuted cone can be obtained by
+ conjugation::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
sage: L = ToricLattice(K.lattice_dim()**2)
sage: p = SymmetricGroup(K.lattice_dim()).random_element().matrix()
sage: pK = Cone([ p*k for k in K ], K.lattice(), check=False)
- sage: Z_of_pK = Z_operator_gens(pK)
- sage: actual = Cone([t.list() for t in Z_of_pK],
+ sage: Sigma_of_pK = cross_positive_operator_gens(pK)
+ sage: actual = Cone([t.list() for t in Sigma_of_pK],
....: lattice=L,
....: check=False)
- sage: Z_of_K = Z_operator_gens(K)
- sage: expected = Cone([(p*t*p.inverse()).list() for t in Z_of_K],
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
+ sage: expected = Cone([ (p*t*p.inverse()).list() for t in Sigma_of_K ],
....: lattice=L,
....: check=False)
sage: actual.is_equivalent(expected)
True
- An operator is a Z-operator on a cone if and only if its
- adjoint is a Z-operator on the dual of that cone::
+ An operator is cross-positive on a cone if and only if its
+ adjoint is cross-positive on the dual of that cone::
sage: set_random_seed()
sage: K = random_cone(max_ambient_dim=4)
sage: n = K.lattice_dim()
sage: L = ToricLattice(n**2)
sage: W = VectorSpace(F, n**2)
- sage: Z_of_K = Z_operator_gens(K)
- sage: Z_of_K_star = Z_operator_gens(K.dual())
- sage: Z_cone = Cone([p.list() for p in Z_of_K],
- ....: lattice=L,
- ....: check=False)
- sage: Z_star = Cone([p.list() for p in Z_of_K_star],
- ....: lattice=L,
- ....: check=False)
+ sage: Sigma_of_K = cross_positive_operator_gens(K)
+ sage: Sigma_of_K_star = cross_positive_operator_gens(K.dual())
+ sage: Sigma_cone = Cone([ p.list() for p in Sigma_of_K ],
+ ....: lattice=L,
+ ....: check=False)
+ sage: Sigma_star = Cone([ p.list() for p in Sigma_of_K_star ],
+ ....: lattice=L,
+ ....: check=False)
sage: M = MatrixSpace(F, n)
- sage: L = M(Z_cone.random_element(ring=QQ).list())
- sage: Z_star.contains(W(L.transpose().list()))
+ sage: L = M(Sigma_cone.random_element(ring=QQ).list())
+ sage: Sigma_star.contains(W(L.transpose().list()))
True
sage: L = W.random_element()
sage: L_star = W(M(L.list()).transpose().list())
- sage: Z_cone.contains(L) == Z_star.contains(L_star)
+ sage: Sigma_cone.contains(L) == Sigma_star.contains(L_star)
True
"""
# Matrices are not vectors in Sage, so we have to convert them
Sigma_cone = Sigma_dual.dual()
# And finally convert its rays back to matrix representations.
- # But first, make them negative, so we get Z-operators and
- # not cross-positive ones.
M = MatrixSpace(F, n)
- return [ -M(v.list()) for v in Sigma_cone ]
+ return [ M(v.list()) for v in Sigma_cone ]
+
+
+def Z_operator_gens(K):
+ r"""
+ Compute generators of the cone of Z-operators on this cone.
+
+ The Z-operators on a cone generalize the Z-matrices over the
+ nonnegative orthant. They are simply negations of the
+ :meth:`cross_positive_operators`.
+
+ OUTPUT:
+
+ A list of `n`-by-``n`` matrices where ``n == K.lattice_dim()``.
+ Each matrix ``L`` in the list should have the property that
+ ``(L*x).inner_product(s) <= 0`` whenever ``(x,s)`` is an element of
+ this cone's :meth:`discrete_complementarity_set`. Moreover, any
+ conic (nonnegative linear) combination of these matrices shares the
+ same property.
+
+ .. SEEALSO::
+
+ :meth:`positive_operator_gens`, :meth:`cross_positive_operator_gens`,
+
+ REFERENCES:
+
+ M. Orlitzky.
+ Positive and Z-operators on closed convex cones.
+
+ TESTS:
+
+ The Z-property is possessed by every Z-operator::
+
+ sage: set_random_seed()
+ sage: K = random_cone(max_ambient_dim=4)
+ sage: Z_of_K = Z_operator_gens(K)
+ sage: dcs = K.discrete_complementarity_set()
+ sage: all([(z*x).inner_product(s) <= 0 for z in Z_of_K
+ ....: for (x,s) in dcs])
+ True
+ """
+ return [ -cp for cp in cross_positive_operator_gens(K) ]
def LL_cone(K):
L = ToricLattice(K.lattice_dim()**2)
return Cone([ g.list() for g in gens ], lattice=L, check=False)
+def Sigma_cone(K):
+ gens = cross_positive_operator_gens(K)
+ L = ToricLattice(K.lattice_dim()**2)
+ return Cone([ g.list() for g in gens ], lattice=L, check=False)
+
def Z_cone(K):
gens = Z_operator_gens(K)
L = ToricLattice(K.lattice_dim()**2)
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