Changeset 7254:f69ced541e37

Timestamp:

11/03/07 11:24:07 (6 years ago)

Author:

William Stein <wstein@…>

Branch:

default

Message:

Fix trac #790 -- rational reconstruction failing for p-adics

File:

• sage/rings/padics/padic_generic_element.pyx (modified) (2 diffs)

sage/rings/padics/padic_generic_element.pyx

@@ -776 +776 @@
     def rational_reconstruction(self):
         r"""
-        Returns a rational approximation to this p-adic number
-
+        Returns the unique rational approximation to this p-adic
+        number with certain properties, or raises a ValueError (see
+        OUTPUT below).  Uses the rational reconstruction algorithm
+        applied to the unit part of this rational number.
+        
         INPUT:
             self -- a p-adic element
+            
         OUTPUT:
-            rational -- an approximation to self
+             Numerator and denominator n, d of the unique rational           
+             number r=n/d, if it exists, with                                
+                |n| and |d| <= sqrt(N/2),
+             where N = p^prec, i.e., where the *unit part* of self
+             is ... + O(p^prec).  If no such r exists, a ValueError
+             is raised. 
+             
         EXAMPLES:
             sage: R = Zp(5,20,'capped-rel')
@@ -789 +799 @@
             ...               continue
             ...           assert i/j == R(i/j).rational_reconstruction()
+
+        A ValueError is raised when a rational reconstruction of
+        the unit part does not exist:
+            sage: R = Zp(5, 5)
+            sage: R(1413*5).rational_reconstruction()
+            Traceback (most recent call last):
+            ...
+            ValueError: Rational reconstruction of 1413 (mod 3125) does not exist.
         """
         if self.is_zero(self.precision_absolute()):