Changeset 488808e in git for libpolys/polys/ext_fields/algext.cc

Timestamp:

May 26, 2011, 12:12:01 PM (13 years ago)

Author:

Frank Seelisch <seelisch@…>

Branches:

(u'spielwiese', '379ec2d037299db64c43fe3550b5ba8fe508dbe5')

Children:

5a4b26f3e00776270c3ba83b16c92a69f3cca0e0

Parents:

73a9ffb72679635d0a4389f31022ac7b37564499

git-author:

Frank Seelisch <seelisch@mathematik.uni-kl.de>2011-05-26 12:12:01+02:00

git-committer:

Mohamed Barakat <mohamed.barakat@rwth-aachen.de>2011-11-09 12:36:53+01:00

Message:

removed calls to nCoeff_is_Q_a and nCoeff_is_Zp_a (kept definitions for compatibility towards svn trunk); changed map in algext.cc

File:

• libpolys/polys/ext_fields/algext.cc (modified) (3 diffs)

libpolys/polys/ext_fields/algext.cc

@@ -87 +87 @@
 void definiteReduce(poly &p, poly reducer, const coeffs cf);
 
+/* returns the bottom field in this field extension tower; if the tower
+   is flat, i.e., if there is no extension, then r itself is returned;
+   as a side-effect, the counter 'height' is filled with the height of
+   the extension tower (in case the tower is flat, 'height' is zero) */
+static coeffs nCoeff_bottom(const coeffs r, int &height)
+{
+  assume(r != NULL);
+  coeffs cf = r;
+  height = 0;
+  while (nCoeff_is_Extension(cf))
+  {
+    assume(cf->algring != NULL); assume(cf->algring->cf != NULL);
+    cf = cf->algring->cf;
+    height++;
+  }
+  return cf;
+}
+
 BOOLEAN naIsZero(number a, const coeffs cf)
 {
@@ -526 +544 @@
 nMapFunc naSetMap(const coeffs src, const coeffs dst)
 {
-  /* dst is expected to be an algebraic extension field */
+  /* dst is expected to be an algebraic field extension */
   assume(getCoeffType(dst) == n_algExt);
   
-  /* ATTENTION: This code assumes that dst is an algebraic extension of Q
-                or Zp. So, dst must NOT BE an algebraic extension of some
-                extension etc. This code will NOT WORK for extension
-                towers of height >= 2. */
-  
-  if (nCoeff_is_Q(src) && nCoeff_is_Q_a(dst))
+  int h = 0; /* the height of the extension tower given by dst */
+  coeffs bDst = nCoeff_bottom(dst, h); /* the bottom field in the tower dst */
+  
+  /* for the time being, we only provide maps if h = 1 and if b is Q or
+     some field Z/pZ: */
+  if (h != 1) return NULL;
+  if ((!nCoeff_is_Zp(bDst)) && (!nCoeff_is_Q(bDst))) return NULL;
+  
+  if (nCoeff_is_Q(src) && nCoeff_is_Q(bDst))
     return naMap00;                                      /// Q     -->  Q(a)
   
-  if (nCoeff_is_Zp(src) && nCoeff_is_Q_a(dst))
+  if (nCoeff_is_Zp(src) && nCoeff_is_Q(bDst))
     return naMapP0;                                      /// Z/p   -->  Q(a)
   
-  if (nCoeff_is_Q_a(src) && nCoeff_is_Q_a(dst))
+  if (nCoeff_is_Q(src) && nCoeff_is_Zp(bDst))
+    return naMap0P;                                      /// Q      --> Z/p(a)
+  
+  if (nCoeff_is_Zp(src) && nCoeff_is_Zp(bDst))
+  {
+    if (src->ch == dst->ch) return naMapPP;              /// Z/p    --> Z/p(a)
+    else return naMapUP;                                 /// Z/u    --> Z/p(a)
+  }
+  
+  coeffs bSrc = nCoeff_bottom(src, h); /* the bottom field in the tower src */
+  if (h != 1) return NULL;
+  if ((!nCoeff_is_Zp(bSrc)) && (!nCoeff_is_Q(bSrc))) return NULL;
+  
+  if (nCoeff_is_Q(bSrc) && nCoeff_is_Q(bDst))
   {
     if (strcmp(rParameter(src->algring)[0],
@@ -549 +583 @@
   }
   
-  if (nCoeff_is_Q(src) && nCoeff_is_Zp_a(dst))
-    return naMap0P;                                      /// Q      --> Z/p(a)
-  
-  if (nCoeff_is_Zp(src) && nCoeff_is_Zp_a(dst))
-  {
-    if (src->ch == dst->ch) return naMapPP;              /// Z/p    --> Z/p(a)
-    else return naMapUP;                                 /// Z/u    --> Z/p(a)
-  }
-  
-  if (nCoeff_is_Zp_a(src) && nCoeff_is_Zp_a(dst))
+  if (nCoeff_is_Zp(bSrc) && nCoeff_is_Zp(bDst))
   {
     if (strcmp(rParameter(src->algring)[0],