Function idSectWithElim

kernel/ideals.cc:132–198

static ideal idSectWithElim (ideal h1,ideal h2, GbVariant alg)
// does not destroy h1,h2
{
  if (TEST_OPT_PROT) PrintS("intersect by elimination method\n");
  assume(!idIs0(h1));
  assume(!idIs0(h2));
  assume(IDELEMS(h1)<=IDELEMS(h2));
  assume(id_RankFreeModule(h1,currRing)==0);
  assume(id_RankFreeModule(h2,currRing)==0);
  // add a new variable:
  int j;
  ring origRing=currRing;
  ring r=rCopy0(origRing);
  r->N++;
  r->block0[0]=1;
  r->block1[0]= r->N;
  omFree(r->order);
  r->order=(rRingOrder_t*)omAlloc0(3*sizeof(rRingOrder_t));
  r->order[0]=ringorder_dp;
  r->order[1]=ringorder_C;
  char **names=(char**)omAlloc0(rVar(r) * sizeof(char_ptr));
  for (j=0;j<r->N-1;j++) names[j]=r->names[j];
  names[r->N-1]=omStrDup("@");
  omFree(r->names);
  r->names=names;
  rComplete(r,TRUE);
  // fetch h1, h2
  ideal h;
  h1=idrCopyR(h1,origRing,r);
  h2=idrCopyR(h2,origRing,r);
  // switch to temp. ring r
  rChangeCurrRing(r);
  // create 1-t, t
  poly omt=p_One(currRing);
  p_SetExp(omt,r->N,1,currRing);
  p_Setm(omt,currRing);
  poly t=p_Copy(omt,currRing);
  omt=p_Neg(omt,currRing);
  omt=p_Add_q(omt,pOne(),currRing);
  // compute (1-t)*h1
  h1=(ideal)mp_MultP((matrix)h1,omt,currRing);
  // compute t*h2
  h2=(ideal)mp_MultP((matrix)h2,pCopy(t),currRing);
  // (1-t)h1 + t*h2
  h=idInit(IDELEMS(h1)+IDELEMS(h2),1);
  int l;
  for (l=IDELEMS(h1)-1; l>=0; l--)
  {
    h->m[l] = h1->m[l];  h1->m[l]=NULL;
  }
  j=IDELEMS(h1);
  for (l=IDELEMS(h2)-1; l>=0; l--)
  {
    h->m[l+j] = h2->m[l];  h2->m[l]=NULL;
  }
  idDelete(&h1);
  idDelete(&h2);
  // eliminate t: