Ticket #4376: 4376_reversion_fixes.patch

sage/rings/fraction_field_element.pyx

@@ -118 +118 @@
             (x + 1)/(x^2 + x + 1)
             sage: K(355/113)
             355/113
+
+        The next example failed before #4376::
+
+            sage: K(pari((x + 1)/(x^2 + x + 1)))
+            (x + 1)/(x^2 + x + 1)
+
         """
         FieldElement.__init__(self, parent)
         if coerce:

sage/rings/polynomial/polynomial_ring.py

@@ -307 +307 @@
                 raise TypeError, "denominator must be a unit"
             
         elif isinstance(x, pari_gen):
+            if x.type() == 't_RFRAC':
+                raise TypeError, "denominator must be a unit"
             if x.type() != 't_POL':
                 x = x.Polrev()
 

sage/rings/power_series_poly.pyx

@@ -751 +751 @@
             sage: g(f)
             t + O(t^4)
 
+            sage: A.<t> = PowerSeriesRing(ZZ)
+            sage: B.<s> = A[[]]
+            sage: f = (1 - 3*t + 4*t^3 + O(t^4))*s + (2 + t + t^2 + O(t^3))*s^2 + O(s^3)
+            sage: set_verbose(1)
+            sage: g = f.reversion(); g
+            verbose 1 (<module>) passing to pari failed; trying Lagrange inversion
+            (1 + 3*t + 9*t^2 + 23*t^3 + O(t^4))*s + (-2 - 19*t - 118*t^2 + O(t^3))*s^2 + O(s^3)
+            sage: set_verbose(0)
+            sage: f(g) == g(f) == s
+            True
 
         If the leading coefficient is not a unit, we pass to its fraction
         field if possible::
@@ -846 +856 @@
             f2 = f._pari_()
             g = f2.serreverse()
             return PowerSeries_poly(f.parent(),g.Vecrev(),out_prec)
-        except (TypeError,ValueError,AttributeError):
+        except (TypeError,ValueError,AttributeError,PariError):
             # if pari fails, continue with Lagrange inversion
             from sage.misc.all import verbose
             verbose("passing to pari failed; trying Lagrange inversion")
@@ -864 +874 @@
             return rev_lift.change_ring(f.base_ring())
         
         t = f.parent().gen()
+        R = f.parent().base_ring()
 
         h = t/f
         k = 1
         g = 0
         for i in range(1, out_prec):
             k *= h
-            g += k.padded_list(i)[i - 1]/i*t**i
+            g += R(k.padded_list(i)[i - 1]/i)*t**i
         g = g.add_bigoh(out_prec)
         return PowerSeries_poly(out_parent, g, out_prec, check=False)