Either ``True`` if ``A`` is doubly-nonnegative, or ``False``
otherwise.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import is_doubly_nonnegative
+
EXAMPLES:
Every completely positive matrix is doubly-nonnegative::
the doubly-nonnegative cone in `$\mathbb{R}^{n}$`, or ``False``
otherwise.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import is_admissible_extreme_rank
+
EXAMPLES:
For dimension 5, only ranks zero, one, and three are admissible::
26 (1996), no. 4, 1371--1383. doi:10.1216/rmjm/1181071993.
http://projecteuclid.org/euclid.rmjm/1181071993.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import has_admissible_extreme_rank
+
EXAMPLES:
The zero matrix has rank zero, which is admissible::
return is_admissible_extreme_rank(r,n)
-def E(matrix_space, i,j):
+def stdE(matrix_space, i,j):
"""
Return the ``i``,``j``th element of the standard basis in
``matrix_space``.
A basis element of ``matrix_space``. It has a single \"1\" in the
``i``,``j`` row,column and zeros elsewhere.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import stdE
+
EXAMPLES::
sage: M = MatrixSpace(ZZ, 2, 2)
- sage: E(M,0,0)
+ sage: stdE(M,0,0)
[1 0]
[0 0]
- sage: E(M,0,1)
+ sage: stdE(M,0,1)
[0 1]
[0 0]
- sage: E(M,1,0)
+ sage: stdE(M,1,0)
[0 0]
[1 0]
- sage: E(M,1,1)
+ sage: stdE(M,1,1)
[0 0]
[0 1]
- sage: E(M,2,1)
+ sage: stdE(M,2,1)
Traceback (most recent call last):
...
IndexError: Index `i` is out of bounds.
- sage: E(M,1,2)
+ sage: stdE(M,1,2)
Traceback (most recent call last):
...
IndexError: Index `j` is out of bounds.
# would be computed as offset 3 into a four-element list and we
# would succeed incorrectly.
idx = matrix_space.ncols()*i + j
- return matrix_space.basis()[idx]
+ return list(matrix_space.basis())[idx]
2. Berman, Abraham and Shaked-Monderer, Naomi. Completely Positive
Matrices. World Scientific, 2003.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import is_extreme_doubly_nonnegative
+
EXAMPLES:
The zero matrix is an extreme matrix::
for i in range(0,j):
if A[i,j] == 0:
M = A.matrix_space()
- S = X.transpose() * (E(M,i,j) + E(M,j,i)) * X
+ S = X.transpose() * (stdE(M,i,j) + stdE(M,j,i)) * X
spanning_set.append(S)
# The spanning set that we have at this point is of matrices. We
A random doubly nonnegative matrix, i.e. a linear transformation
from ``V`` to itself.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import (is_doubly_nonnegative,
+ ....: random_doubly_nonnegative)
+
EXAMPLES:
Well, it doesn't crash at least::
A random extreme doubly nonnegative matrix, i.e. a linear
transformation from ``V`` to itself.
+ SETUP::
+
+ sage: from mjo.cone.doubly_nonnegative import (is_extreme_doubly_nonnegative,
+ ....: random_extreme_doubly_nonnegative)
+
EXAMPLES:
Well, it doesn't crash at least::