Changeset 865b20 in git for libpolys/polys

Timestamp:

Aug 15, 2012, 7:55:06 PM (12 years ago)

Author:

Oleksandr Motsak <motsak@…>

Branches:

(u'spielwiese', 'fe61d9c35bf7c61f2b6cbf1b56e25e2f08d536cc')

Children:

0beffdffc2fb65355384c180d0a9d06b7b0312cf

Parents:

6caad65fe9bcc8eacbc315b1b090770683668e8e

git-author:

Oleksandr Motsak <motsak@mathematik.uni-kl.de>2012-08-15 19:55:06+02:00

git-committer:

Oleksandr Motsak <motsak@mathematik.uni-kl.de>2012-08-15 19:59:03+02:00

Message:

fixed a bug in naInvers for the case of non-irreducible minpoly and division by a zero-divisor

File:

• libpolys/polys/ext_fields/algext.cc (modified) (2 diffs)

libpolys/polys/ext_fields/algext.cc

@@ -394 +394 @@
   if (a == NULL) return NULL;
   poly bInverse = (poly)naInvers(b, cf);
-  poly aDivB = p_Mult_q(p_Copy((poly)a, naRing), bInverse, naRing);
-  definiteReduce(aDivB, naMinpoly, cf);
-  return (number)aDivB;
+  if(bInverse != NULL) // b is non-zero divisor!
+  {
+    poly aDivB = p_Mult_q(p_Copy((poly)a, naRing), bInverse, naRing);
+    definiteReduce(aDivB, naMinpoly, cf);
+    return (number)aDivB;
+  }
+  return NULL;
 }
 
@@ -655 +659 @@
   naTest(a);
   if (a == NULL) WerrorS(nDivBy0);
+  
   poly aFactor = NULL; poly mFactor = NULL;
   poly theGcd = p_ExtGcd((poly)a, aFactor, naMinpoly, mFactor, naRing);
+  
   naTest((number)theGcd); naTest((number)aFactor); naTest((number)mFactor);
-  /* the gcd must be 1 since naMinpoly is irreducible and a != NULL: */
-  assume(naIsOne((number)theGcd, cf));
+  p_Delete(&mFactor, naRing);
+  
+  //  /* the gcd must be 1 since naMinpoly is irreducible and a != NULL: */
+  //  assume(naIsOne((number)theGcd, cf)); 
+
+  if( !naIsOne((number)theGcd, cf) )
+  {  
+    WerrorS("zero divisor found - your minpoly is not irreducible");
+    p_Delete(&aFactor, naRing); aFactor = NULL;
+  }
   p_Delete(&theGcd, naRing);
-  p_Delete(&mFactor, naRing);
+
   return (number)(aFactor);
 }