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A.22 Normalization

The normalization will be computed for a reduced ring R∕I . The result is a list of rings; ideals are always called norid in the rings of this list. The normalization of R∕I is the product of the factor rings of the rings in the list divided out by the ideals norid.

  LIB "normal.lib";
  // ----- first example: rational quadruple point -----
  ring R=32003,(x,y,z),wp(3,5,15);
  ideal I=z*(y3-x5)+x10;
  list pr=normal(I);
→ 
→ // 'normal' created a list of 1 ring(s).
→ // nor[1+1] is the delta-invariant in case of choose=wd.
→ // To see the rings, type (if the name of your list is nor):
→      show( nor);
→ // To access the 1-st ring and map (similar for the others), type:
→      def R = nor[1]; setring R;  norid; normap;
→ // R/norid is the 1-st ring of the normalization and
→ // normap the map from the original basering to R/norid
  def S=pr[1];
  setring S;
  norid;
→ norid[1]=T(2)*T(3)-T(1)*T(4)
→ norid[2]=T(1)^7-T(1)^2*T(3)+T(2)*T(5)
→ norid[3]=T(1)^2*T(5)-T(2)*T(4)
→ norid[4]=T(1)^5*T(4)-T(3)*T(4)+T(5)^2
→ norid[5]=T(1)^6*T(3)-T(1)*T(3)^2+T(4)*T(5)
→ norid[6]=T(1)*T(3)*T(5)-T(4)^2
  // ----- second example: union of straight lines -----
  ring R1=0,(x,y,z),dp;
  ideal I=(x-y)*(x-z)*(y-z);
  list qr=normal(I);
→ 
→ // 'normal' created a list of 3 ring(s).
→ // nor[3+1] is the delta-invariant in case of choose=wd.
→ // To see the rings, type (if the name of your list is nor):
→      show( nor);
→ // To access the 1-st ring and map (similar for the others), type:
→      def R = nor[1]; setring R;  norid; normap;
→ // R/norid is the 1-st ring of the normalization and
→ // normap the map from the original basering to R/norid
  def S1=qr[1]; def S2=qr[2];
  setring S1; norid;
→ norid[1]=0
  setring S2; norid;
→ norid[1]=0

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