X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Fhurwitz.py;h=07eace64fd9e9a92e93a937d3ee9a4352089442b;hb=HEAD;hp=ccc8219b1a92036c6ac92f118339c160a885977b;hpb=d0c6baf5cd567617f96a2a598123052409b33c94;p=sage.d.git

diff --git a/mjo/hurwitz.py b/mjo/hurwitz.py
index ccc8219..07eace6 100644
--- a/mjo/hurwitz.py
+++ b/mjo/hurwitz.py
@@ -23,7 +23,6 @@ class Octonion(IndexedFreeModuleElement):
 
         Conjugating twice gets you the original element::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: x.conjugate().conjugate() == x
@@ -58,7 +57,6 @@ class Octonion(IndexedFreeModuleElement):
 
         This method is idempotent::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: x.real().real() == x.real()
@@ -91,7 +89,6 @@ class Octonion(IndexedFreeModuleElement):
 
         This method is idempotent::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: x.imag().imag() == x.imag()
@@ -121,7 +118,6 @@ class Octonion(IndexedFreeModuleElement):
 
         The norm is nonnegative and belongs to the base field::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: n = O.random_element().norm()
             sage: n >= 0 and n in O.base_ring()
@@ -129,7 +125,6 @@ class Octonion(IndexedFreeModuleElement):
 
         The norm is homogeneous::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: alpha = O.base_ring().random_element()
@@ -167,7 +162,6 @@ class Octonion(IndexedFreeModuleElement):
 
         TESTS::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: x.is_zero() or ( x*x.inverse() == O.one() )
@@ -241,7 +235,6 @@ class Octonions(CombinatorialFreeModule):
 
         This gives the correct unit element::
 
-            sage: set_random_seed()
             sage: O = Octonions()
             sage: x = O.random_element()
             sage: x*O.one() == x and O.one()*x == x
@@ -306,25 +299,158 @@ class Octonions(CombinatorialFreeModule):
 
 
 class HurwitzMatrixAlgebraElement(MatrixAlgebraElement):
+    def conjugate(self):
+        r"""
+        Return the entrywise conjugate of this matrix.
+
+        SETUP::
+
+            sage: from mjo.hurwitz import ComplexMatrixAlgebra
+
+        EXAMPLES::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [ I,   1 + 2*I],
+            ....:         [ 3*I,     4*I] ])
+            sage: M.conjugate()
+            +------+----------+
+            | -I   | -2*I + 1 |
+            +------+----------+
+            | -3*I | -4*I     |
+            +------+----------+
+
+        ::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, QQ)
+            sage: M = A([ [ 1, 2],
+            ....:         [ 3, 4] ])
+            sage: M.conjugate() == M
+            True
+            sage: M.to_vector()
+            (1, 0, 2, 0, 3, 0, 4, 0)
+
+        """
+        d = self.monomial_coefficients()
+        A = self.parent()
+        new_terms = ( A._conjugate_term((k,v)) for (k,v) in d.items() )
+        return self.parent().sum_of_terms(new_terms)
+
+    def conjugate_transpose(self):
+        r"""
+        Return the conjugate-transpose of this matrix.
+
+        SETUP::
+
+            sage: from mjo.hurwitz import ComplexMatrixAlgebra
+
+        EXAMPLES::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [ I,   2*I],
+            ....:         [ 3*I, 4*I] ])
+            sage: M.conjugate_transpose()
+            +------+------+
+            | -I   | -3*I |
+            +------+------+
+            | -2*I | -4*I |
+            +------+------+
+            sage: M.conjugate_transpose().to_vector()
+            (0, -1, 0, -3, 0, -2, 0, -4)
+
+        """
+        d = self.monomial_coefficients()
+        A = self.parent()
+        new_terms = ( A._conjugate_term( ((k[1],k[0],k[2]), v) )
+                      for (k,v) in d.items() )
+        return self.parent().sum_of_terms(new_terms)
+
     def is_hermitian(self):
         r"""
 
         SETUP::
 
-            sage: from mjo.hurwitz import HurwitzMatrixAlgebra
+            sage: from mjo.hurwitz import (ComplexMatrixAlgebra,
+            ....:                          HurwitzMatrixAlgebra)
 
         EXAMPLES::
 
-            sage: A = HurwitzMatrixAlgebra(2, QQbar, ZZ)
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
             sage: M = A([ [ 0,I],
             ....:         [-I,0] ])
             sage: M.is_hermitian()
             True
 
+        ::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [ 0,0],
+            ....:         [-I,0] ])
+            sage: M.is_hermitian()
+            False
+
+        ::
+
+            sage: A = HurwitzMatrixAlgebra(2, AA, QQ)
+            sage: M = A([ [1, 1],
+            ....:         [1, 1] ])
+            sage: M.is_hermitian()
+            True
+
         """
+        # A tiny bit faster than checking equality with the conjugate
+        # transpose.
         return all( self[i,j] == self[j,i].conjugate()
                     for i in range(self.nrows())
-                    for j in range(self.ncols()) )
+                    for j in range(i+1) )
+
+
+    def is_skew_symmetric(self):
+        r"""
+        Return whether or not this matrix is skew-symmetric.
+
+        SETUP::
+
+            sage: from mjo.hurwitz import (ComplexMatrixAlgebra,
+            ....:                          HurwitzMatrixAlgebra)
+
+        EXAMPLES::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [ 0,I],
+            ....:         [-I,1] ])
+            sage: M.is_skew_symmetric()
+            False
+
+        ::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [   0, 1+I],
+            ....:         [-1-I,   0] ])
+            sage: M.is_skew_symmetric()
+            True
+
+        ::
+
+            sage: A = HurwitzMatrixAlgebra(2, AA, QQ)
+            sage: M = A([ [1, 1],
+            ....:         [1, 1] ])
+            sage: M.is_skew_symmetric()
+            False
+
+        ::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [2*I   ,  1 + I],
+            ....:         [-1 + I, -2*I] ])
+            sage: M.is_skew_symmetric()
+            False
+
+        """
+        # A tiny bit faster than checking equality with the negation
+        # of the transpose.
+        return all( self[i,j] == -self[j,i]
+                    for i in range(self.nrows())
+                    for j in range(i+1) )
 
 
 class HurwitzMatrixAlgebra(MatrixAlgebra):
@@ -352,6 +478,45 @@ class HurwitzMatrixAlgebra(MatrixAlgebra):
 
         super().__init__(n, entry_algebra, scalars, **kwargs)
 
+
+    @staticmethod
+    def _conjugate_term(t):
+        r"""
+        Conjugate the given ``(index, coefficient)`` term, returning
+        another such term.
+
+        Given a term ``((i,j,e), c)``, it's straightforward to
+        conjugate the entry ``e``, but if ``e``-conjugate is ``-e``,
+        then the resulting ``((i,j,-e), c)`` is not a term, since
+        ``(i,j,-e)`` is not a monomial index! So when we build a sum
+        of these conjugates we can wind up with a nonsense object.
+
+        This function handles the case where ``e``-conjugate is
+        ``-e``, but nothing more complicated. Thus it makes sense in
+        Hurwitz matrix algebras, but not more generally.
+
+        SETUP::
+
+            sage: from mjo.hurwitz import ComplexMatrixAlgebra
+
+        EXAMPLES::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ)
+            sage: M = A([ [ I,   1 + 2*I],
+            ....:         [ 3*I,     4*I] ])
+            sage: t = list(M.monomial_coefficients().items())[1]
+            sage: t
+            ((1, 0, I), 3)
+            sage: A._conjugate_term(t)
+            ((1, 0, I), -3)
+
+        """
+        if t[0][2].conjugate() == t[0][2]:
+            return t
+        else:
+            return (t[0], -t[1])
+
+
     def entry_algebra_gens(self):
         r"""
         Return a tuple of the generators of (that is, a basis for) the
@@ -490,7 +655,6 @@ class OctonionMatrixAlgebra(HurwitzMatrixAlgebra):
 
     TESTS::
 
-        sage: set_random_seed()
         sage: A = OctonionMatrixAlgebra(ZZ.random_element(10))
         sage: x = A.random_element()
         sage: x*A.one() == x and A.one()*x == x
@@ -583,7 +747,6 @@ class QuaternionMatrixAlgebra(HurwitzMatrixAlgebra):
 
     TESTS::
 
-        sage: set_random_seed()
         sage: A = QuaternionMatrixAlgebra(ZZ.random_element(10))
         sage: x = A.random_element()
         sage: x*A.one() == x and A.one()*x == x
@@ -599,6 +762,32 @@ class QuaternionMatrixAlgebra(HurwitzMatrixAlgebra):
             entry_algebra = QuaternionAlgebra(scalars,-1,-1)
         super().__init__(n, entry_algebra, scalars, **kwargs)
 
+    def _entry_algebra_element_to_vector(self, entry):
+        r"""
+
+        SETUP::
+
+            sage: from mjo.hurwitz import QuaternionMatrixAlgebra
+
+        EXAMPLES::
+
+            sage: A = QuaternionMatrixAlgebra(2)
+            sage: u = A.entry_algebra().one()
+            sage: A._entry_algebra_element_to_vector(u)
+            (1, 0, 0, 0)
+            sage: i,j,k = A.entry_algebra().gens()
+            sage: A._entry_algebra_element_to_vector(i)
+            (0, 1, 0, 0)
+            sage: A._entry_algebra_element_to_vector(j)
+            (0, 0, 1, 0)
+            sage: A._entry_algebra_element_to_vector(k)
+            (0, 0, 0, 1)
+
+        """
+        from sage.modules.free_module import FreeModule
+        d = len(self.entry_algebra_gens())
+        V = FreeModule(self.entry_algebra().base_ring(), d)
+        return V(entry.coefficient_tuple())
 
 class ComplexMatrixAlgebra(HurwitzMatrixAlgebra):
     r"""
@@ -650,11 +839,11 @@ class ComplexMatrixAlgebra(HurwitzMatrixAlgebra):
         sage: (I,) = A.entry_algebra().gens()
         sage: A([ [1+I, 1],
         ....:     [-1, -I] ])
-        +-------+----+
-        | I + 1 | 1  |
-        +-------+----+
-        | -1    | -I |
-        +-------+----+
+        +---------+------+
+        | 1 + 1*I | 1    |
+        +---------+------+
+        | -1      | -1*I |
+        +---------+------+
 
     ::
 
@@ -667,7 +856,6 @@ class ComplexMatrixAlgebra(HurwitzMatrixAlgebra):
 
     TESTS::
 
-        sage: set_random_seed()
         sage: A = ComplexMatrixAlgebra(ZZ.random_element(10))
         sage: x = A.random_element()
         sage: x*A.one() == x and A.one()*x == x
@@ -679,3 +867,24 @@ class ComplexMatrixAlgebra(HurwitzMatrixAlgebra):
             from sage.rings.all import QQbar
             entry_algebra = QQbar
         super().__init__(n, entry_algebra, scalars, **kwargs)
+
+    def _entry_algebra_element_to_vector(self, entry):
+        r"""
+
+        SETUP::
+
+            sage: from mjo.hurwitz import ComplexMatrixAlgebra
+
+        EXAMPLES::
+
+            sage: A = ComplexMatrixAlgebra(2, QQbar, QQ)
+            sage: A._entry_algebra_element_to_vector(QQbar(1))
+            (1, 0)
+            sage: A._entry_algebra_element_to_vector(QQbar(I))
+            (0, 1)
+
+        """
+        from sage.modules.free_module import FreeModule
+        d = len(self.entry_algebra_gens())
+        V = FreeModule(self.entry_algebra().base_ring(), d)
+        return V((entry.real(), entry.imag()))