-# Sage doesn't load ~/.sage/init.sage during testing (sage -t), so we
-# have to explicitly mangle our sitedir here so that "mjo.cone"
-# resolves.
-from os.path import abspath
-from site import addsitedir
-addsitedir(abspath('../../'))
-
from sage.all import *
-from mjo.cone.cone import lyapunov_rank
-def rearrangement_cone(p,n):
+def rearrangement_cone(p,n,lattice=None):
r"""
Return the rearrangement cone of order ``p`` in ``n`` dimensions.
INPUT:
- - ``p`` -- The number of components to "rearrange."
+ - ``p`` -- The number of components to "rearrange."
+
+ - ``n`` -- The dimension of the ambient space for the resulting cone.
- - ``n`` -- The dimension of the ambient space for the resulting cone.
+ - ``lattice`` -- (default: ``None``) an ambient lattice of rank ``n``
+ to be passed to the :func:`Cone` constructor.
OUTPUT:
A polyhedral closed convex cone object representing a rearrangement
- cone of order ``p`` in ``n`` dimensions.
+ cone of order ``p`` in ``n`` dimensions. Each generating ray will
+ have the integer ring as its base ring.
+
+ If a ``lattice`` was specified, then the resulting cone will live in
+ that lattice unless its rank is incompatible with the dimension
+ ``n`` (in which case a ``ValueError`` is raised).
+
+ ALGORITHM:
+
+ The generators for the rearrangement cone are given by [Jeong]_
+ Theorem 5.2.3.
+
+ REFERENCES:
+
+ .. [GowdaJeong] Muddappa Seetharama Gowda and Juyoung Jeong.
+ Spectral cones in Euclidean Jordan algebras.
+ Linear Algebra and its Applications, 509, 286-305.
+ doi:10.1016/j.laa.2016.08.004
+
+ .. [HenrionSeeger] Rene Henrion and Alberto Seeger.
+ Inradius and Circumradius of Various Convex Cones Arising in
+ Applications. Set-Valued and Variational Analysis, 18(3-4),
+ 483-511, 2010. doi:10.1007/s11228-010-0150-z
+
+ .. [Jeong] Juyoung Jeong.
+ Spectral sets and functions on Euclidean Jordan algebras.
+ University of Maryland, Baltimore County, Ph.D. thesis, 2017.
+
+ SETUP::
+
+ sage: from mjo.cone.rearrangement import rearrangement_cone
EXAMPLES:
sage: rearrangement_cone(5,5).lineality()
4
- All rearrangement cones are proper::
+ All rearrangement cones are proper when ``p`` is less than ``n`` by
+ [Jeong]_ Proposition 5.2.1::
- sage: all([ rearrangement_cone(p,n).is_proper()
- ....: for n in range(10)
- ....: for p in range(n) ])
+ sage: all( rearrangement_cone(p,n).is_proper()
+ ....: for n in range(10)
+ ....: for p in range(1, n) )
True
The Lyapunov rank of the rearrangement cone of order ``p`` in ``n``
- dimensions is ``n`` for ``p == 1`` or ``p == n`` and one otherwise::
+ dimensions is ``n`` for ``p == 1`` or ``p == n`` and one otherwise,
+ by [Jeong]_ Corollary 5.2.4::
- sage: all([ lyapunov_rank(rearrangement_cone(p,n)) == n
- ....: for n in range(2, 10)
- ....: for p in [1, n-1] ])
+ sage: all( rearrangement_cone(p,n).lyapunov_rank() == n
+ ....: for n in range(2, 10)
+ ....: for p in [1, n-1] )
True
- sage: all([ lyapunov_rank(rearrangement_cone(p,n)) == 1
- ....: for n in range(3, 10)
- ....: for p in range(2, n-1) ])
+ sage: all( rearrangement_cone(p,n).lyapunov_rank() == 1
+ ....: for n in range(3, 10)
+ ....: for p in range(2, n-1) )
True
TESTS:
- The rearrangement cone is permutation-invariant::
+ All rearrangement cones are permutation-invariant by [Jeong]_
+ Proposition 5.2.1::
sage: n = ZZ.random_element(2,10).abs()
sage: p = ZZ.random_element(1,n)
sage: K = rearrangement_cone(p,n)
sage: P = SymmetricGroup(n).random_element().matrix()
- sage: all([ K.contains(P*r) for r in K.rays() ])
+ sage: all( K.contains(P*r) for r in K )
True
- """
+ The smallest ``p`` components of every element of the rearrangement
+ cone should sum to a nonnegative number (this tests that the
+ generators really are what we think they are)::
+
+ sage: def _has_rearrangement_property(v,p):
+ ....: return sum( sorted(v)[0:p] ) >= 0
+ sage: all( _has_rearrangement_property(
+ ....: rearrangement_cone(p,n).random_element(),
+ ....: p
+ ....: )
+ ....: for n in range(2, 10)
+ ....: for p in range(1, n-1)
+ ....: )
+ True
- def d(j):
- v = [1]*n # Create the list of all ones...
- v[j] = 1 - p # Now "fix" the ``j``th entry.
- return v
+ The rearrangenent cone of order ``p`` is contained in the rearrangement
+ cone of order ``p + 1`` by [Jeong]_ Proposition 5.2.1::
- V = VectorSpace(QQ, n)
- G = V.basis() + [ d(j) for j in range(n) ]
- return Cone(G)
+ sage: n = ZZ.random_element(2,10)
+ sage: p = ZZ.random_element(1,n)
+ sage: K1 = rearrangement_cone(p,n)
+ sage: K2 = rearrangement_cone(p+1,n)
+ sage: all( x in K2 for x in K1 )
+ True
+
+ The rearrangement cone of order ``p`` is linearly isomorphic to the
+ rearrangement cone of order ``n - p`` when ``p`` is less than ``n``,
+ by [Jeong]_ Proposition 5.2.1::
+
+ sage: n = ZZ.random_element(2,10)
+ sage: p = ZZ.random_element(1,n)
+ sage: K1 = rearrangement_cone(p,n)
+ sage: K2 = rearrangement_cone(n-p, n)
+ sage: Mp = (1/p)*matrix.ones(QQ,n) - identity_matrix(QQ,n)
+ sage: Cone( (Mp*K2.rays()).columns() ).is_equivalent(K1)
+ True
+
+ The order ``p`` should be between ``1`` and ``n``, inclusive::
+
+ sage: rearrangement_cone(0,3)
+ Traceback (most recent call last):
+ ...
+ ValueError: order p=0 should be between 1 and n=3, inclusive
+ sage: rearrangement_cone(5,3)
+ Traceback (most recent call last):
+ ...
+ ValueError: order p=5 should be between 1 and n=3, inclusive
+
+ If a ``lattice`` was given, it is actually used::
+
+ sage: L = ToricLattice(3, 'M')
+ sage: rearrangement_cone(2, 3, lattice=L)
+ 3-d cone in 3-d lattice M
+
+ Unless the rank of the lattice disagrees with ``n``::
+
+ sage: L = ToricLattice(1, 'M')
+ sage: rearrangement_cone(2, 3, lattice=L)
+ Traceback (most recent call last):
+ ...
+ ValueError: lattice rank=1 and dimension n=3 are incompatible
+
+ """
+ if p < 1 or p > n:
+ raise ValueError('order p=%d should be between 1 and n=%d, inclusive'
+ %
+ (p,n))
+
+ if lattice is None:
+ lattice = ToricLattice(n)
+
+ if lattice.rank() != n:
+ raise ValueError('lattice rank=%d and dimension n=%d are incompatible'
+ %
+ (lattice.rank(), n))
+
+ I = identity_matrix(ZZ,n)
+ M = matrix.ones(ZZ,n) - p*I
+ G = identity_matrix(ZZ,n).rows() + M.rows()
+ return Cone(G, lattice=lattice)
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