Ticket #11780: trac11780_unique_auxiliar_polyring.patch

sage/libs/singular/ring.pyx

@@ -35 +35 @@
 
 from sage.rings.polynomial.term_order import TermOrder
 from sage.rings.polynomial.multi_polynomial_libsingular cimport MPolynomial_libsingular, MPolynomialRing_libsingular
+from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
 
 
 from sage.misc.misc_c import is_64_bit
@@ -172 +173 @@
         else:
             raise TypeError, "characteristic must be <= 2147483647."
         # TODO: This is lazy, it should only call Singular stuff not MPolynomial stuff
-        k = MPolynomialRing_libsingular(base_ring.prime_subfield(), 1, base_ring.variable_name(), 'lex')
+        try:
+            k = PolynomialRing(base_ring.prime_subfield(), 1, [base_ring.variable_name()], 'lex')
+        except TypeError:
+            raise TypeError, "The multivariate polynomial ring in a single variable %s in lex order over %s is supposed to be of type %s"%(base_ring.variable_name(), base_ring,MPolynomialRing_libsingular)
         minpoly = base_ring.polynomial()(k.gen())
         is_extension = True
 
     elif PY_TYPE_CHECK(base_ring, NumberField) and base_ring.is_absolute():
         characteristic = 1
-        k = MPolynomialRing_libsingular(RationalField(), 1, base_ring.variable_name(), 'lex')
+        try:
+            k = PolynomialRing(RationalField(), 1, [base_ring.variable_name()], 'lex')
+        except TypeError:
+            raise TypeError, "The multivariate polynomial ring in a single variable %s in lex order over Rational Field is supposed to be of type %s"%(base_ring.variable_name(), MPolynomialRing_libsingular)
         minpoly = base_ring.polynomial()(k.gen())
         is_extension = True
 

sage/rings/polynomial/multi_polynomial_libsingular.pyx

@@ -4781 +4781 @@
             sage: f.numerator().base_ring()
             Integer Ring
     
-        We check that the computation the numerator and denominator
-        are valid
+        We check that the computation of numerator and denominator
+        is valid.
     
         ::
     
@@ -4790 +4790 @@
             sage: f=K.random_element()
             sage: f.numerator() / f.denominator() == f
             True
+
+        The following tests against a bug that has been fixed in trac ticket #11780::
+
+            sage: P.<foo,bar> = ZZ[]
+            sage: Q.<foo,bar> = QQ[]
+            sage: f = Q.random_element()
+            sage: f.numerator().parent() is P
+            True
         """
         if self.base_ring() == RationalField():
             #This part is for compatibility with the univariate case,
             #where the numerator of a polynomial over RationalField
             #is a polynomial over IntegerRing
-            integer_polynomial_ring = MPolynomialRing_libsingular(ZZ,\
+            #
+            # Trac ticket #11780: Create the polynomial ring over
+            # the integers using the (cached) polynomial ring constructor:
+            from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
+            integer_polynomial_ring = PolynomialRing(ZZ,\
             self.parent().ngens(), self.parent().gens(), order =\
             self.parent().term_order())
             return integer_polynomial_ring(self * self.denominator())