Changeset 7441:5b6d6e2e4a87

Timestamp:

11/14/07 15:24:07 (6 years ago)

Author:

dmharvey@…

Branch:

default

Message:

partially addresses trac #1134 by creating fast QQ => numberfield_quadratic coercion

Location:

sage/rings/number_field

Files:

• number_field.py (modified) (1 diff)
• number_field_element_quadratic.pyx (modified) (3 diffs)

sage/rings/number_field/number_field.py

@@ -4551 +4551 @@
         parts = -b/(2*a), (Dpoly/D).sqrt()/(2*a)
         self._NumberField_generic__gen = self._element_class(self, parts)
+
+
+    def coerce_map_from_impl(self, S):
+        """
+        EXAMPLES:
+            sage: K.<a> = QuadraticField(-3)
+            sage: f = K.coerce_map_from(QQ); f
+            Natural morphism:
+              From: Rational Field
+              To:   Number Field in a with defining polynomial x^2 + 3
+            sage: f(3/5)
+            3/5
+            sage: parent(f(3/5)) is K
+            True
+        """
+        if S is QQ:
+            return number_field_element_quadratic.Q_to_quadratic_field_element(self)
+        else:
+            return NumberField_absolute.coerce_map_from_impl(self, S)
+
+
         
     def discriminant(self, v=None):

sage/rings/number_field/number_field_element_quadratic.pyx

@@ -5 +5 @@
     -- Robert Bradshaw (2007-09): Initial version
     -- David Harvey (2007-10): fix up a few bugs, polish around the edges
+
+TODO:
+    the _new() method should be overridden in this class to copy the D attribute
+
 """
 #*****************************************************************************
@@ -36 +40 @@
 from sage.rings.rational_field import QQ
 from sage.rings.integer_ring import ZZ
+from sage.categories.morphism cimport Morphism
 
 
@@ -935 +940 @@
         res._reduce_c_()
         return res
+
+
+
+cdef class Q_to_quadratic_field_element(Morphism):
+    """
+    Morphism that coerces from rationals to elements of a
+    quadratic number field K.
+    """
+    cdef NumberFieldElement_quadratic zero_element    # the zero element of K
+    
+    def __init__(self, K):
+        """ K is the target quadratic field """
+        import sage.categories.homset
+        Morphism.__init__(self, sage.categories.homset.Hom(QQ, K))
+        self.zero_element = PY_NEW(NumberFieldElement_quadratic)
+        self.zero_element._parent = K
+        self.zero_element.D = K._D
+        
+
+    cdef Element _call_c_impl(self, Element x):
+        cdef NumberFieldElement_quadratic y = self.zero_element._new()
+        y.D = self.zero_element.D
+        mpz_set(y.a, mpq_numref((<Rational>x).value))
+        mpz_set(y.denom, mpq_denref((<Rational>x).value))
+        return y
+
+    def _repr_type(self):
+        return "Natural"