source: git/Singular/LIB/swalk.lib @ 0dd77c2

version="$Id$";
category="Commutative Algebra";
info="
LIBRARY: swalk.lib               Sagbi Walk Conversion Algorithm
AUTHOR:  Junaid Alam Khan        junaidalamkhan@gmail.com

OVERVIEW:
 A library for computing the Sagbi basis of subalgebra through Sagbi walk
 algorithm.

THEORY: The concept of SAGBI ( Subalgebra Analog to Groebner Basis for Ideals)
 is defined in [L. Robbiano, M. Sweedler: Subalgebra Bases, volume 42, volume
 1430 of Lectures Note in Mathematics series, Springer-Verlag (1988),61-87].
 The Sagbi Walk algorithm is the subalgebra analogue to the Groebner Walk
 algorithm which has been proposed in [S. Collart, M. Kalkbrener and D.Mall:
 Converting bases with the Grobner Walk. J. Symbolic Computation 24 (1997),
 465-469].

PROCEDURE:
 swalk(ideal[,intvec]);   Sagbi basis of subalgebra via Sagbi walk algorithm
";

LIB "sagbi.lib";
//////////////////////////////////////////////////////////////////////////////
proc swalk(ideal Gox, list #)
"USAGE:  swalk(i[,v,w]); i ideal, v,w int vectors
RETURN: The sagbi basis of the subalgebra defined by the generators of i,
        calculated via the Sagbi walk algorithm from the ordering dp to lp
        if v,w are not given (resp. from the ordering (a(v),lp) to the
        ordering (a(w),lp) if v and w are given).
EXAMPLE: example swalk; shows an example
"
{
  /* we use ring with ordering (a(...),lp,C) */
  list OSCTW    = OrderStringalp_NP("al", #);//"dp"
  string ord_str =   OSCTW[2];
  intvec icurr_weight   =   OSCTW[3]; /* original weight vector */
  intvec itarget_weight =   OSCTW[4]; /* terget weight vector */
  kill OSCTW;
  option(redSB);
  def xR = basering;
  list rl=ringlist(xR);
  rl[3][1][1]="dp";
  def ostR=ring(rl);
  setring ostR;
  def new_ring = basering;
  ideal Gnew = fetch(xR, Gox);
  Gnew=sagbi(Gnew,1);
  Gnew=interreduceSd(Gnew);
  vector curr_weight=changeTypeInt(icurr_weight);
  vector target_weight=changeTypeInt(itarget_weight);
  ideal Gold;
  list l;
  intvec v;
  int n=0;
  while(n==0)
    {
       Gold=Gnew;
       def old_ring=new_ring;
       setring old_ring;
       number ulast;
       kill new_ring;
       if(curr_weight==target_weight){n=1;}
       else {
              l=collectDiffExpo(Gold);
              ulast=last(curr_weight, target_weight, l);
              vector new_weight=(1-ulast)*curr_weight+ulast*target_weight;
              vector w=cleardenom(new_weight);
              v=changeType(w);
              list p= ringlist(old_ring);
              p[3][1][2]= v;
              def new_ring=ring(p);
              setring new_ring;
              ideal Gold=fetch(old_ring,Gold);
              vector curr_weight=fetch(old_ring,new_weight);
              vector target_weight=fetch(old_ring,target_weight);
              kill old_ring;
              ideal Gnew=Convert(Gold);
              Gnew=interreduceSd(Gnew);
           }
    }
   setring xR;
   ideal result = fetch(old_ring, Gnew);
   attrib(result,"isSB",1);
   return (result);
}
example
{
  "EXAMPLE:";echo = 2;
  ring r = 0,(x,y), lp;
  ideal I =x2,y2,xy+y,2xy2+y3;
  swalk(I);
}

//////////////////////////////////////////////////////////////////////////////
static proc inprod(vector v,vector w)
"USAGE:  inprod(v,w); v,w vectors
RETURN:  inner product of vector v and w
EXAMPLE: example inprod; shows an example
"
{
  poly a;
  int i;
  for(i=1;i<=nvars(basering);i++)
    {
      a=a+v[i]*w[i] ;
    }
  return(a);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   vector v =[1,-1,2];
   vector w = [1,0,3];
   inprod(v,w);
}

//////////////////////////////////////////////////////////////////////////////
static proc diffExpo(poly f)
"USAGE:  diffExpo(f); f polynomial
RETURN:  a list of integers vectors which are the difference of exponent
         vector of leading monomial of f with the exponent vector of of other
         monmials in f.
EXAMPLE: example diffExpo; shows an example
"
{
  list l;
  int i;
  intvec v;
  for(i=size(f);i>=2;i--)
   {
     v=leadexp(f[1])-leadexp(f[i]);
     l[i-1]=v;
   }
 return(l);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   poly f = xy+z2 ;
   diffExpo(f);
}

//////////////////////////////////////////////////////////////////////////////
static proc collectDiffExpo( ideal i)
"USAGE:  collectDiffExpo(i); i ideal
RETURN:  a list which contains diffExpo(f), for all generators f of ideal i
EXAMPLE: example collectDiffExpo; shows an example
"
{
 list l;
 int j;
 for(j=ncols(i); j>=1;j--)
  {
   l[j]=diffExpo(i[j]);
  }
  return(l);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   ideal I = xy+z2,y3+x2y2;
   collectDiffExpo(I);
}

//////////////////////////////////////////////////////////////////////////////
static proc changeType(vector v)
"USAGE:  changeType(v); v  vector
RETURN:  change the type of  vector
         v into integer vector.

EXAMPLE: example changeType; shows an example
"
{
  intvec w ;
  int j ;
  for(j=1;j<=nvars(basering);j++)
   {
     w[j]=int(leadcoef(v[j]));
   }
  return(w);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   vector v = [2,1,3];
   changeType(v);
}
//////////////////////////////////////////////////////////////////////////////
static proc changeTypeInt( intvec v)
"USAGE:  changeTypeInt(v); v integer vector
RETURN:  change the type of integer vector v into vector.
EXAMPLE: example changeTypeInt; shows an example
"
{
   vector w;
   int j ;
   for(j=1;j<=size(v);j++)
   {
     w=w+v[j]*gen(j);
   }
   return(w);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   intvec v = 4,2,3;
   changeTypeInt(v);
}

//////////////////////////////////////////////////////////////////////////////
static proc last( vector c, vector t,list l)
"USAGE: last(c,t,l); c,t vectors, l list
RETURN: a  parametric value which corresponds to vector lies along the path
        between c and t using list l of integer vectors. This vector is the
        last vector on old Sagbi cone
EXAMPLE: example last; shows an example
"
{
 number ul=1;
 int i,j,k;
 number u;
 vector v;
 for(i=1;i<=size(l);i++)
 {
    for(j=1;j<=size(l[i]);j++)
    {
        v=0;
        for(k=1;k<=size(l[i][j]);k++)
        {
            v=v+l[i][j][k]*gen(k);
        }
        poly n= inprod(c,v);
        poly q= inprod(t,v);
        number a=leadcoef(n);
        number b=leadcoef(q);
        number z=a-b;
        if(b<0)
        {
            u=a/z;
            if(u<ul) {ul=u;}
        }
        kill a,b,z,n,q ;
    }
 }
 return(ul);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),(a(0,0,1),lp);
   vector v= [0,0,1];
   vector w=[1,0,0];
   ideal i=z2+xy,x2y2+y3;
    list l=collectDiffExpo(i);
    last(v,w,l)
}

//////////////////////////////////////////////////////////////////////////////
static proc initialForm(poly P)
"USAGE:  initialForm(P); P polynomial
RETURN:  sum of monomials of P with maximum w-degree
         where w is first row of matrix of a given monomial ordering
EXAMPLE: example initialForm; shows an example
"
{
 poly q;
 int i=1;
 while(deg(P[i])==deg(P[1]))
 {
     q=q+P[i];
     i++;
     if(i>size(P)) {break;}
 }
 return(q);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),dp;
   poly f = x2+yz+z;
   initialForm(f);
}

//////////////////////////////////////////////////////////////////////////////
static proc Initial(ideal I)
"USAGE:  Initial(I); I ideal
RETURN:  an ideal which is generate by the InitialForm
         of the generators of I.
EXAMPLE: example Initial; shows an example
"
{
 ideal J;
 int i;
 for(i=1;i<=ncols(I);i++)
 {
     J[i]=initialForm(I[i]);
 }
 return(J);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),dp;
   ideal I = x+1,x+y+1;
   Initial(I);
}

//////////////////////////////////////////////////////////////////////////////
static proc Lift(ideal In,ideal InG,ideal Gold)
"USAGE:  Lift(In, InG, Gold); In, InG, Gold ideals;
         Gold given by Sagbi basis {g_1,...,g_t},
         In given by tne initial forms In(g_1),...,In(g_t),
         InG = {h_1,...,h_s} a Sagbi basis of In
RETURN:  P_j, a polynomial in K[y_1,..,y_t] such that h_j =
         P_j(In(g_1),...,In_(g_t))
         and return f_j = P_j(g_1,...,g_t)
EXAMPLE: example Lift; shows an example
"
{
  int i;
  ideal J;
  for(i=1;i<=ncols(InG);i++)
  {
    poly f=InG[i];
    list l=algebra_containment(f,In,1);
    def s=l[2];
    map F=s,maxideal(1),Gold ;
    poly g=F(check);
    ideal k=g;
    J=J+k;
    kill g,l,s,F,f,k;
  }
  return(J);
 }
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),(a(2,0,3),lp);
   ideal In = xy+z2,x2y2;
   ideal InG=xy+z2,x2y2,xyz2+1/2z4;
   ideal Gold=xy+z2,y3+x2y2;
   Lift(In,InG,Gold);
}

//////////////////////////////////////////////////////////////////////////////
static proc Convert( ideal Gold )
"USAGE: Convert(I); I ideal
RETURN: Convert old Sagbi basis into new Sagbi basis
EXAMPLE: example Convert; shows an example
"
{
 ideal In=Initial(Gold);
 ideal InG=sagbi(In,1)+In;
 ideal Gnew=Lift(In,InG,Gold);
 return(Gnew);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   ideal I=xy+z2, y3+x2y2;
   Convert(I);
}

//////////////////////////////////////////////////////////////////////////////
static proc interreduceSd(ideal I)
"USAGE:  interreduceSd(I); I ideal
RETURN:  interreduceSd the set of generators if I with
         respect to a given term ordering
EXAMPLE: example interreduceSd; shows an example
"
{
  list l,M;
  ideal J,B;
  int i,j,k;
  poly f;
  for(k=1;k<=ncols(I);k++)
  {l[k]=I[k];}
  for(j=1;j<=size(l);j++)
  {
     f=l[j];
     M=delete(l,j);
     for(i=1;i<=size(M);i++)
     { B[i]=M[i];}
     f=sagbiNF(f,B,1);
     J=J+f;
  }
  return(J);
}
example
{ "EXAMPLE:"; echo = 2;
   ring r=0,(x,y,z),lp;
   ideal I = xy+z2,x2y2+y3;
   interreduceSd(I);
}

//////////////////////////////////////////////////////////////////////////////
static proc OrderStringalp(string Wpal,list #)
{
  int n= nvars(basering);
  string order_str;
  intvec curr_weight, target_weight;
  curr_weight = system("Mivdp",n);
  target_weight = system("Mivlp",n);

   if(size(#) != 0)
   {
     if(size(#) == 1)
     {
       if(typeof(#[1]) == "intvec")
       {
         if(Wpal == "al"){
           order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
         }
         else {
           order_str = "(Wp("+string(#[1])+"),C)";
         }
         curr_weight = #[1];
       }
       else
       {
        if(typeof(#[1]) == "string")
        {
          if(#[1] == "Dp") {
            order_str = "Dp";
          }
          else {
            order_str = "dp";
          }
        }
        else {
          order_str = "dp";
        }
     }
    }
    else
    {
     if(size(#) == 2)
     {
       if(typeof(#[2]) == "intvec")
       {
         target_weight = #[2];
       }
       if(typeof(#[1]) == "intvec")
       {
         if(Wpal == "al"){
           order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
         }
         else {
           order_str = "(Wp("+string(#[1])+"),C)";
         }
         curr_weight = #[1];
       }
       else
       {
        if(typeof(#[1]) == "string")
        {
          if(#[1] == "Dp") {
            order_str = "Dp";
           }
           else {
              order_str = "dp";
           }
        }
        else {
           order_str = "dp";
        }
      }
     }
    }
   }
   else {
     order_str = "dp";
   }
   list result;
   result[1] = order_str;
   result[2] = curr_weight;
   result[3] = target_weight;
   return(result);
}

//////////////////////////////////////////////////////////////////////////////
static proc OrderStringalp_NP(string Wpal,list #)
{
  int n= nvars(basering);
  string order_str = "dp";
  int nP = 1;// call LatsGB to compute the wanted GB  by pwalk
  intvec curr_weight = system("Mivdp",n); //define (1,1,...,1)
  intvec target_weight = system("Mivlp",n); //define (1,0,...,0)
  if(size(#) != 0)
  {
    if(size(#) == 1)
    {
      if(typeof(#[1]) == "intvec")
      {
        curr_weight = #[1];

        if(Wpal == "al")
        {
          order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
        }
        else
        {
          order_str = "(Wp("+string(#[1])+"),C)";
        }
      }
      else {
        if(typeof(#[1]) == "int")
        {
          nP = #[1];
        }
        else
        {
          print("// ** the input must be \"(ideal, int)\" or ");
          print("// **                   \"(ideal, intvec)\"");
          print("// ** a lex. GB will be computed from \"dp\" to \"lp\"");
        }
      }
    }
    else
    {
     if(size(#) == 2)
     {
       if(typeof(#[1]) == "intvec" and typeof(#[2]) == "int")
       {
         curr_weight = #[1];

         if(Wpal == "al")
         {
           order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
         }
         else
         {
           order_str = "(Wp("+string(#[1])+"),C)";
         }
       }
       else
       {
         if(typeof(#[1]) == "intvec" and typeof(#[2]) == "intvec")
         {
           curr_weight = #[1];
           target_weight = #[2];

           if(Wpal == "al")
           {
             order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
           }
           else
           {
             order_str = "(Wp("+string(#[1])+"),C)";
           }
         }
         else
         {
           print("// ** the input  must be \"(ideal,intvec,int)\" or ");
           print("// **                    \"(ideal,intvec,intvec)\"");
           print("// ** and a lex. GB will be computed from \"dp\" to \"lp\"");
         }
       }
     }
     else {
       if(size(#) == 3)
       {
         if(typeof(#[1]) == "intvec" and typeof(#[2]) == "intvec" and
            typeof(#[3]) == "int")
         {
           curr_weight = #[1];
           target_weight = #[2];
           nP = #[3];
           if(Wpal == "al")
           {
             order_str = "(a("+string(#[1])+"),lp("+string(n) + "),C)";
           }
           else
           {
             order_str = "(Wp("+string(#[1])+"),C)";
           }
         }
         else
         {
           print("// ** the input must be \"(ideal,intvec,intvec,int)\"");
           print("// ** and a lex. GB will be computed from \"dp\" to \"lp\"");

         }
       }
       else
       {
         print("// ** The given input is wrong");
         print("// ** and a lex. GB will be computed from \"dp\" to \"lp\"");
       }
     }
    }
  }
  list result;
  result[1] = nP;
  result[2] = order_str;
  result[3] = curr_weight;
  result[4] = target_weight;
  return(result);
}

///////////////////////////////////////////////////////////////////////////////*
Further examples
ring r=0,(x,y,z),lp;

ideal I=x2y4, y4z2, xy4z+y2z, xy6z2+y10z5;

ideal Q=x2y4, y4z2, xy4z+y2z, xy6z2+y14z7;

ideal J=x2y4, y4z2, xy4z+y2z, xy6z2+y18z9;

ideal K=x2,y2,xy+y,2xy2+y5,z3+x;

ideal L=x2+y,y2+z,x+z2;
*/