source: git/Singular/LIB/ncfactor.lib @ 6e40beb

////////////////////////////////////////////////////////////////////////////////////////////////////
version = "$Id: ncfactor.lib, v 1.00 2010/02/15 10:06 heinle Exp $";
category="Noncommutative";
info="
LIBRARY: ncfactor.lib   Tools for factorization in the first Weyl algebra
AUTHORS: Albert Heinle,     albert.heinle@rwth-aachen.de

MAIN PROCEDURES:
homogfac(h);         computes one factorization of a homogeneous polynomial h
homogfac_all(h);     computes all factorizations of a homogeneous polynomial h
facwa(h);            computes all factorizations of an inhomogeneous polynomial h

/* ring R = 0,(x,y),Ws(-1,1); */
/* def r = nc_algebra(1,1); */
/* setring(r); */
";
LIB "general.lib";
LIB "nctools.lib";
LIB "involut.lib";

////////////////////////////////////////////////////////////////////////////////////////////////////
//==================================================*
//deletes double-entries in a list of factorization
//without evaluating the product.
static proc delete_dublicates_noteval(list l)
{//proc delete_dublicates_noteval
     list result= l;
     int j; int k; int i;
     int deleted = 0;
     int is_equal;
     for (i = 1; i<= size(l); i++)
     {//Iterate over the different factorizations
          for (j = i+1; j<= size(l); j++)
          {//Compare the i'th factorization to the j'th
               if (size(l[i])!= size(l[j]))
               {//different sizes => not equal
                    j++;
                    continue;
               }//different sizes => not equal
               is_equal = 1;
               for (k = 1; k <= size(l[i]);k++)
               {//Compare every entry
                    if (l[i][k]!=l[j][k])
                    {
                         is_equal = 0;
                         break;
                    }
               }//Compare every entry
               if (is_equal == 1)
               {//Delete this entry, because there is another equal one int the list
                    result = delete(result, i-deleted);
                    deleted = deleted+1;
                    break;
               }//Delete this entry, because there is another equal one int the list
          }//Compare the i'th factorization to the j'th
     }//Iterate over the different factorizations
     return(result);
}//proc delete_dublicates_noteval

//==================================================
//deletes the double-entries in a list with
//evaluating the products
static proc delete_dublicates_eval(list l)
{//proc delete_dublicates_eval
     list result=l;
     int j; int k; int i;
     int deleted = 0;
     int is_equal;
     for (i = 1; i<= size(result); i++)
     {//Iterating over all elements in result
          for (j = i+1; j<= size(result); j++)
          {//comparing with the other elements
               if (product(result[i]) == product(result[j]))
               {//There are two equal results; throw away that one with the smaller size
                    if (size(result[i])>=size(result[j]))
                    {//result[i] has more entries
                         result = delete(result,j);
                         continue;
                    }//result[i] has more entries
                    else
                    {//result[j] has more entries
                         result = delete(result,i);
                         i--;
                         break;
                    }//result[j] has more entries
               }//There are two equal results; throw away that one with the smaller size
          }//comparing with the other elements
     }//Iterating over all elements in result
     return(result);
}//proc delete_dublicates_eval


//==================================================*
//given a list of factors g and a desired size nof, the following
//procedure combines the factors, such that we recieve a
//list of the length nof.
static proc combinekfinlf(list g, int nof, intvec limits) //nof stands for "number of factors"
{//Procedure combinekfinlf
     list result;
     int i; int j; int k; //iteration variables
     list fc; //fc stands for "factors combined"
     list temp; //a temporary store for factors
     def nofgl = size(g); //nofgl stands for "number of factors of the given list"
     if (nofgl == 0)
     {//g was the empty list
          return(result);
     }//g was the empty list
     if (nof <= 0)
     {//The user wants to recieve a negative number or no element as a result
          return(result);
     }//The user wants to recieve a negative number or no element as a result
     if (nofgl == nof)
     {//There are no factors to combine
          if (limitcheck(g,limits))
          {
               result = result + list(g);
          }
          return(result);
     }//There are no factors to combine
     if (nof == 1)
     {//User wants to get just one factor
          if (limitcheck(list(product(g)),limits))
          {
               result = result + list(list(product(g)));
          }
          return(result);
     }//User wants to get just one factor
     for (i = nof; i > 1; i--)
     {//computing the possibilities that have at least one original factor from g
          for (j = i; j>=1; j--)
          {//shifting the window of combinable factors to the left
               fc = combinekfinlf(list(g[(j)..(j+nofgl - i)]),nof - i + 1,limits); //fc stands for "factors combined"
               for (k = 1; k<=size(fc); k++)
               {//iterating over the different solutions of the smaller problem
                    if (j>1)
                    {//There are g_i before the combination
                         if (j+nofgl -i < nofgl)
                         {//There are g_i after the combination
                              temp = list(g[1..(j-1)]) + fc[k] + list(g[(j+nofgl-i+1)..nofgl]);
                         }//There are g_i after the combination
                         else
                         {//There are no g_i after the combination
                              temp = list(g[1..(j-1)]) + fc[k];
                         }//There are no g_i after the combination
                    }//There are g_i before the combination
                    if (j==1)
                    {//There are no g_i before the combination
                         if (j+ nofgl -i <nofgl)
                         {//There are g_i after the combination
                              temp = fc[k]+ list(g[(j + nofgl - i +1)..nofgl]);
                         }//There are g_i after the combination
                    }//There are no g_i before the combination
                    if (limitcheck(temp,limits))
                    {
                         result = result + list(temp);
                    }
               }//iterating over the different solutions of the smaller problem
          }//shifting the window of combinable factors to the left
     }//computing the possibilities that have at least one original factor from g
     for (i = 2; i<=nofgl/nof;i++)
     {//getting the other possible results
          result = result + combinekfinlf(list(product(list(g[1..i])))+list(g[(i+1)..nofgl]),nof,limits);
     }//getting the other possible results
     result = delete_dublicates_noteval(result);
     return(result);
}//Procedure combinekfinlf


//==================================================*
//merges two sets of factors ignoring common
//factors
static proc merge_icf(list l1, list l2, intvec limits)
{//proc merge_icf
     list g;
     list f;
     int i; int j;
     if (size(l1)==0)
     {
          return(list());
     }
     if (size(l2)==0)
     {
          return(list());
     }
     if (size(l2)<=size(l1))
     {//l1 will be our g, l2 our f
          g = l1;
          f = l2;
     }//l1 will be our g, l2 our f
     else
     {//l1 will be our f, l2 our g
          g = l2;
          f = l1;
     }//l1 will be our f, l2 our g
     def result = combinekfinlf(g,size(f),limits);
     for (i = 1 ; i<= size(result); i++)
     {//Adding the factors of f to every possibility listed in temp
          for (j = 1; j<= size(f); j++)
          {
               result[i][j] = result[i][j]+f[j];
          }
          if(!limitcheck(result[i],limits))
          {
               result = delete(result,i);
               i--;
          }
     }//Adding the factors of f to every possibility listed in temp
     return(result);
}//proc merge_icf

//==================================================*
//merges two sets of factors with respect to the occurrence
//of common factors
static proc merge_cf(list l1, list l2, intvec limits)
{//proc merge_cf
     list g;
     list f;
     int i; int j;
     list pre;
     list post;
     list candidate;
     list temp;
     int temppos;
     if (size(l1)==0)
     {//the first list is empty
          return(list());
     }//the first list is empty
     if(size(l2)==0)
     {//the second list is empty
          return(list());
     }//the second list is empty
     if (size(l2)<=size(l1))
     {//l1 will be our g, l2 our f
          g = l1;
          f = l2;
     }//l1 will be our g, l2 our f
     else
     {//l1 will be our f, l2 our g
          g = l2;
          f = l1;
     }//l1 will be our f, l2 our g
     list M;
     for (i = 2; i<size(f); i++)
     {//finding common factors of f and g...
        for (j=2; j<size(g);j++)
        {//... with g
             if (f[i] == g[j])
             {//we have an equal pair
                  M = M + list(list(i,j));
             }//we have an equal pair
        }//... with g
     }//finding common factors of f and g...
     if (g[1]==f[1])
     {//Checking for the first elements to be equal
          M = M + list(list(1,1));
     }//Checking for the first elements to be equal
     if (g[size(g)]==f[size(f)])
     {//Checking for the last elements to be equal
          M = M + list(list(size(f),size(g)));
     }//Checking for the last elements to be equal
     list result;//= list(list());
     while(size(M)>0)
     {//set of equal pairs is not empty
          temp = M[1];
          temppos = 1;
          for (i = 2; i<=size(M); i++)
          {//finding the minimal element of M
               if (M[i][1]<=temp[1])
               {//a possible candidate that is smaller than temp could have been found
                    if (M[i][1]==temp[1])
                    {//In this case we must look at the second number
                         if (M[i][2]< temp[2])
                         {//the candidate is smaller
                              temp = M[i];
                              temppos = i;
                         }//the candidate is smaller
                    }//In this case we must look at the second number
                    else
                    {//The candidate is definately smaller
                         temp = M[i];
                         temppos = i;
                    }//The candidate is definately smaller
               }//a possible candidate that is smaller than temp could have been found
          }//finding the minimal element of M
          M = delete(M, temppos);
          if(temp[1]>1)
          {//There are factors to combine before the equal factor
               if (temp[1]<size(f))
               {//The most common case
                    //first the combinations ignoring common factors
                    pre = merge_icf(list(f[1..(temp[1]-1)]),list(g[1..(temp[2]-1)]),limits);
                    post = merge_icf(list(f[(temp[1]+1)..size(f)]),list(g[(temp[2]+1..size(g))]),limits);
                    for (i = 1; i <= size(pre); i++)
                    {//all possible pre's...
                         for (j = 1; j<= size(post); j++)
                         {//...combined with all possible post's
                              candidate = pre[i]+list(f[temp[1]])+post[j];
                              if (limitcheck(candidate,limits))
                              {
                                   result = result + list(candidate);
                              }
                         }//...combined with all possible post's
                    }//all possible pre's...
                    //Now the combinations with respect to common factors
                    post = merge_cf(list(f[(temp[1]+1)..size(f)]),list(g[(temp[2]+1..size(g))]),limits);
                    if (size(post)>0)
                    {//There are factors to combine
                         for (i = 1; i <= size(pre); i++)
                         {//all possible pre's...
                              for (j = 1; j<= size(post); j++)
                              {//...combined with all possible post's
                                   candidate= pre[i]+list(f[temp[1]])+post[j];
                                   if (limitcheck(candidate,limits))
                                   {
                                        result = result + list(candidate);
                                   }
                              }//...combined with all possible post's
                         }//all possible pre's...
                    }//There are factors to combine
               }//The most common case
               else
               {//the last factor is the common one
                    pre = merge_icf(list(f[1..(temp[1]-1)]),list(g[1..(temp[2]-1)]),limits);
                    for (i = 1; i<= size(pre); i++)
                    {//iterating over the possible pre-factors
                         candidate = pre[i]+list(f[temp[1]]);
                         if (limitcheck(candidate,limits))
                         {
                              result = result + list(candidate);
                         }
                    }//iterating over the possible pre-factors
               }//the last factor is the common one
          }//There are factors to combine before the equal factor
          else
          {//There are no factors to combine before the equal factor
               if (temp[1]<size(f))
               {//Just a check for security
                    //first without common factors
                    post=merge_icf(list(f[(temp[1]+1)..size(f)]),list(g[(temp[2]+1..size(g))]),limits);
                    for (i = 1; i<=size(post); i++)
                    {
                         candidate = list(f[temp[1]])+post[i];
                         if (limitcheck(candidate,limits))
                         {
                              result = result + list(candidate);
                         }
                    }
                    //Now with common factors
                    post = merge_cf(list(f[(temp[1]+1)..size(f)]),list(g[(temp[2]+1..size(g))]),limits);
                    if(size(post)>0)
                    {//we could find other combinations
                         for (i = 1; i<=size(post); i++)
                         {
                              candidate = list(f[temp[1]])+post[i];
                              if (limitcheck(candidate,limits))
                              {
                                   result = result + list(candidate);
                              }
                         }
                    }//we could find other combinations
               }//Just a check for security
          }//There are no factors to combine before the equal factor
     }//set of equal pairs is not empty
     return(result);
}//proc merge_cf


//==================================================*
//merges two sets of factors

static proc mergence(list l1, list l2, intvec limits)
{//Procedure mergence
     list g;
     list f;
     int l; int k;
     list F;
     if (size(l2)<=size(l1))
     {//l1 will be our g, l2 our f
          g = l1;
          f = l2;
     }//l1 will be our g, l2 our f
     else
     {//l1 will be our f, l2 our g
          g = l2;
          f = l1;
     }//l1 will be our f, l2 our g
     list result;
     for (l = size(f); l>=1; l--)
     {//all possibilities to combine the factors of f
          F = combinekfinlf(f,l,limits);
          for (k = 1; k<= size(F);k++)
          {//for all possibilities of combinations of the factors of f
               result = result + merge_cf(F[k],g,limits);
               result = result + merge_icf(F[k],g,limits);
          }//for all possibilities of combinations of the factors of f
     }//all possibilities to combine the factors of f
     return(result);
}//Procedure mergence


//==================================================
//Checks, whether a list of factors doesn't exceed the given limits
static proc limitcheck(list g, intvec limits)
{//proc limitcheck
     int i;
     if (size(limits)!=3)
     {//check the input
          return(0);
     }//check the input
     if(size(g)==0)
     {
          return(0);
     }
     def prod = product(g);
     def limg = intvec(deg(prod,intvec(1,1)) ,deg(prod,intvec(1,0)),deg(prod,intvec(0,1)));
     for (i = 1; i<=size(limg);i++)
     {//the final check
          if(limg[i]>limits[i])
          {
               return(0);
          }
     }//the final check
     return(1);
}//proc limitcheck


//==================================================*
//one factorization of a homogeneous polynomial
//in the first Weyl Algebra
proc homogfac(poly h)
"USAGE: homogfac(h); h is a homogeneous polynomial in the first Weyl algebra with respect to the weight vector [-1,1]
RETURN: list
PURPOSE: Computes a factorization of a homogeneous polynomial h with respect to the weight vector [-1,1] in the first Weyl algebra
THEORY: @code{homogfac} returns a list with a factorization of the given, homogeneous polynomial. If the degree of the polynomial is k with k positive, the last k entries in the output list are the second variable. If k is positive, the last k entries will be x. The other entries will be irreducible polynomials of degree zero or 1 resp. -1.
EXAMPLE: example homogfac; shows examples
SEE ALSO: homogfac_all
"{//proc homogfac
     if (!isWeyl())
     {//Our basering is not the Weyl algebra
          return(list());
     }//Our basering is not the Weyl algebra
     if(nvars(basering)!=2)
     {//Our basering is the Weyl algebra, but not the first
          return(list());
     }//Our basering is the Weyl algebra, but not the first
     def r = basering;
     poly hath;
     int i; int j;
     if (!homogwithorder(h,intvec(-1,1)))
     {//The given polynomial is not homogeneous
          return(list());
     }//The given polynomial is not homogeneous
     if (h==0)
     {
          return(list(0));
     }
     list result;
     int m = deg(h,intvec(-1,1));
     if (m!=0)
     {//The degree is not zero
          if (m <0)
          {//There are more x than y
               hath = lift(var(1)^(-m),h)[1,1];
               for (i = 1; i<=-m; i++)
               {
                    result = result + list(var(1));
               }
          }//There are more x than y
          else
          {//There are more y than x
               hath = lift(var(2)^m,h)[1,1];
               for (i = 1; i<=m;i++)
               {
                    result = result + list(var(2));
               }
          }//There are more y than x
     }//The degree is not zero
     else
     {//The degree is zero
          hath = h;
     }//The degree is zero
     //beginning to transform x^i*y^i in teta(teta-1)...(teta-i+1)
     list mons;
     for(i = 1; i<=size(hath);i++)
     {//Putting the monomials in a list
          mons = mons+list(hath[i]);
     }//Putting the monomials in a list
     ring tempRing = 0,(x,y,teta),dp;
     setring tempRing;
     map tetamap = r,x,y;
     list mons = tetamap(mons);
     poly entry;
     for (i = 1; i<=size(mons);i++)
     {//transforming the monomials as monomials in theta
          entry = leadcoef(mons[i]);
          for (j = 0; j<leadexp(mons[i])[2];j++)
          {
               entry = entry * (teta-j);
          }
          mons[i] = entry;
     }//transforming the monomials as monomials in theta
     list azeroresult = factorize(sum(mons));
     list azeroresult_return_form;
     for (i = 1; i<=size(azeroresult[1]);i++)
     {//rewrite the result of the commutative factorization
          for (j = 1; j <= azeroresult[2][i];j++)
          {
               azeroresult_return_form = azeroresult_return_form + list(azeroresult[1][i]);
          }
     }//rewrite the result of the commutative factorization
     setring(r);
     map finalmap = tempRing,var(1),var(2),var(1)*var(2);
     list tempresult = finalmap(azeroresult_return_form);
     for (i = 1; i<=size(tempresult);i++)
     {//factorizations of theta resp. theta +1
          if(tempresult[i]==var(1)*var(2))
          {
               tempresult = insert(tempresult,var(1),i-1);
               i++;
               tempresult[i]=var(2);
          }
          if(tempresult[i]==var(2)*var(1))
          {
               tempresult = insert(tempresult,var(2),i-1);
               i++;
               tempresult[i]=var(1);
          }
     }//factorizations of theta resp. theta +1
     result = tempresult+result;
     return(result);
}//proc homogfac
example
{
     "EXAMPLE:";echo=2;
     ring R = 0,(x,y),Ws(-1,1);
     def r = nc_algebra(1,1);
     setring(r);
     poly h = (x^2*y^2+1)*(x^4);
     homogfac(h);
}

//==================================================
//Computes all possible homogeneous factorizations
proc homogfac_all(poly h)
"USAGE: homogfac_all(h); h is a homogeneous polynomial in the first Weyl algebra with respect to the weight vector [-1,1]
RETURN: list
PURPOSE: Computes all factorizations of a homogeneous polynomial h with respect to the weight vector [-1,1] in the first Weyl algebra
THEORY: @code{homogfac} returns a list with all factorization of the given, homogeneous polynomial. It uses the output of homogfac and permutes its entries with respect to the commutation rule. Furthermore, if a factor of degree zero is irreducible in K[\theta], but reducible in the first Weyl algebra, the permutations of this element with the other entries will also be computed.
EXAMPLE: example homogfac; shows examples
SEE ALSO: homogfac
"{//proc HomogFacAll
     if (deg(h,intvec(1,1)) <= 0 )
     {//h is a constant
          return(list(list(h)));
     }//h is a constant
     if (!isWeyl())
     {//Our basering is not the Weyl algebra
          return(list());
     }//Our basering is not the Weyl algebra
     if(nvars(basering)!=2)
     {//Our basering is the Weyl algebra, but not the first
          return(list());
     }//Our basering is the Weyl algebra, but not the first
     def r = basering;
     list one_hom_fac; //stands for one homogeneous factorization
     int i; int j; int k;
     //Compute again a homogeneous factorization
     one_hom_fac = homogfac(h);
     if (size(one_hom_fac) == 0)
     {//there is no homogeneous factorization or the polynomial was not homogeneous
          return(list());
     }//there is no homogeneous factorization or the polynomial was not homogeneous
     //divide list in A0-Part and a list of x's resp. y's
     list list_not_azero = list();
     list list_azero;
     list k_factor;
     int is_list_not_azero_empty = 1;
     int is_list_azero_empty = 1;
     k_factor = list(one_hom_fac[1]);
     if (absValue(deg(h,intvec(-1,1)))<size(one_hom_fac)-1)
     {//There is a nontrivial A_0-part
          list_azero = one_hom_fac[2..(size(one_hom_fac)-absValue(deg(h,intvec(-1,1))))];
          is_list_azero_empty = 0;
     }//There is a nontrivial A_0 part
     for (i = 1; i<=size(list_azero)-1;i++)
     {//in homogfac, we factorized theta, and this will be made undone
          if (list_azero[i] == var(1))
          {
               if (list_azero[i+1]==var(2))
               {
                    list_azero[i] = var(1)*var(2);
                    list_azero = delete(list_azero,i+1);
               }
          }
          if (list_azero[i] == var(2))
          {
               if (list_azero[i+1]==var(1))
               {
                    list_azero[i] = var(2)*var(1);
                    list_azero = delete(list_azero,i+1);
               }
          }
     }//in homogfac, we factorized theta, and this will be made undone
     if(deg(h,intvec(-1,1))!=0)
     {//list_not_azero is not empty
          list_not_azero = one_hom_fac[(size(one_hom_fac)-absValue(deg(h,intvec(-1,1)))+1)..size(one_hom_fac)];
          is_list_not_azero_empty = 0;
     }//list_not_azero is not empty
     //Map list_azero in K[theta]
     ring tempRing = 0,(x,y,theta), dp;
     setring(tempRing);
     poly entry;
     map thetamap = r,x,y;
     if(!is_list_not_azero_empty)
     {//Mapping in Singular is only possible, if the list before contained at least one element of the other ring
          list list_not_azero = thetamap(list_not_azero);
     }//Mapping in Singular is only possible, if the list before contained at least one element of the other ring
     if(!is_list_azero_empty)
     {//Mapping in Singular is only possible, if the list before contained at least one element of the other ring
          list list_azero= thetamap(list_azero);
     }//Mapping in Singular is only possible, if the list before contained at least one element of the other ring
     list k_factor = thetamap(k_factor);
     list tempmons;
     for(i = 1; i<=size(list_azero);i++)
     {//rewrite the polynomials in A1 as polynomials in K[theta]
          tempmons = list();
          for (j = 1; j<=size(list_azero[i]);j++)
          {
               tempmons = tempmons + list(list_azero[i][j]);
          }
          for (j = 1 ; j<=size(tempmons);j++)
          {
               entry = leadcoef(tempmons[j]);
               for (k = 0; k < leadexp(tempmons[j])[2];k++)
               {
                    entry = entry*(theta-k);
               }
               tempmons[j] = entry;
          }
          list_azero[i] = sum(tempmons);
     }//rewrite the polynomials in A1 as polynomials in K[theta]
     //Compute all permutations of the A0-part
     list result;
     int shift_sign;
     int shift;
     poly shiftvar;
     if (size(list_not_azero)!=0)
     {//Compute all possibilities to permute the x's resp. the y's in the list
          if (list_not_azero[1] == x)
          {//h had a negative weighted degree
               shift_sign = 1;
               shiftvar = x;
          }//h had a negative weighted degree
          else
          {//h had a positive weighted degree
               shift_sign = -1;
               shiftvar = y;
          }//h had a positive weighted degree
          result = permpp(list_azero + list_not_azero);
          for (i = 1; i<= size(result); i++)
          {//adjust the a_0-parts
               shift = 0;
               for (j=1; j<=size(result[i]);j++)
               {
                    if (result[i][j]==shiftvar)
                    {
                         shift = shift + shift_sign;
                    }
                    else
                    {
                         result[i][j] = subst(result[i][j],theta,theta + shift);
                    }
               }
          }//adjust the a_0-parts
     }//Compute all possibilities to permute the x's resp. the y's in the list
     else
     {//The result is just all the permutations of the a_0-part
          result = permpp(list_azero);
     }//The result is just all the permutations of the a_0 part
     if (size(result)==0)
     {
          return(result);
     }
     //Now we are going deeper and search for theta resp. theta + 1, substitute them by xy resp. yx and go on permuting
     int found_theta;
     int thetapos;
     list leftpart;
     list rightpart;
     list lparts;
     list rparts;
     list tempadd;
     for (i = 1; i<=size(result) ; i++)
     {//checking every entry of result for theta or theta +1
          found_theta = 0;
          for(j=1;j<=size(result[i]);j++)
          {
               if (result[i][j]==theta)
               {//the jth entry is theta and can be written as x*y
                    thetapos = j;
                    result[i]= insert(result[i],x,j-1);
                    j++;
                    result[i][j] = y;
                    found_theta = 1;
                    break;
               }//the jth entry is theta and can be written as x*y
               if(result[i][j] == theta +1)
               {
                    thetapos = j;
                    result[i] = insert(result[i],y,j-1);
                    j++;
                    result[i][j] = x;
                    found_theta = 1;
                    break;
               }
          }
          if (found_theta)
          {//One entry was theta resp. theta +1 
               leftpart = result[i];
               leftpart = leftpart[1..thetapos];
               rightpart = result[i];
               rightpart = rightpart[(thetapos+1)..size(rightpart)];
               lparts = list(leftpart);
               rparts = list(rightpart);
               //first deal with the left part
               if (leftpart[thetapos] == x)
               {
                    shift_sign = 1;
                    shiftvar = x;
               }
               else
               {
                    shift_sign = -1;
                    shiftvar = y;
               }
               for (j = size(leftpart); j>1;j--)
               {//drip x resp. y
                    if (leftpart[j-1]==shiftvar)
                    {//commutative
                         j--;
                         continue;
                    }//commutative
                    if (deg(leftpart[j-1],intvec(-1,1,0))!=0)
                    {//stop here
                         break;
                    }//stop here
                    //Here, we can only have a a0- part
                    leftpart[j] = subst(leftpart[j-1],theta, theta + shift_sign);
                    leftpart[j-1] = shiftvar;
                    lparts = lparts + list(leftpart);
                }//drip x resp. y
                //and now deal with the right part
                if (rightpart[1] == x)
                {
                     shift_sign = 1;
                     shiftvar = x;
                }
                else
                {
                     shift_sign = -1;
                     shiftvar = y;
                }
                for (j = 1 ; j < size(rightpart); j++)
                {
                     if (rightpart[j+1] == shiftvar)
                     {
                          j++;
                          continue;
                     }
                     if (deg(rightpart[j+1],intvec(-1,1,0))!=0)
                     {
                          break;
                     }
                     rightpart[j] = subst(rightpart[j+1], theta, theta - shift_sign);
                     rightpart[j+1] = shiftvar;
                     rparts = rparts + list(rightpart);
                }
                //And now, we put all possibilities together
                tempadd = list();
                for (j = 1; j<=size(lparts); j++)
                {
                   for (k = 1; k<=size(rparts);k++)
                   {
                              tempadd = tempadd + list(lparts[j]+rparts[k]);
                   }
                }
                tempadd = delete(tempadd,1); // The first entry is already in the list
                result = result + tempadd;
                continue; //We can may be not be done already with the ith entry
          }//One entry was theta resp. theta +1
     }//checking every entry of result for theta or theta +1
     //map back to the basering
     setring(r);
     map finalmap = tempRing, var(1), var(2),var(1)*var(2);
     list result = finalmap(result);
     for (i=1; i<=size(result);i++)
     {//adding the K factor
          result[i] = k_factor + result[i];
     }//adding the k-factor
     result = delete_dublicates_noteval(result);
     return(result);
}//proc HomogFacAll
example
{
     "EXAMPLE:";echo=2;
     ring R = 0,(x,y),Ws(-1,1);
     def r = nc_algebra(1,1);
     setring(r);
     poly h = (x^2*y^2+1)*(x^4);
     homogfac_all(h);
}

//==================================================*
//Computes all permutations of a given list
static proc perm(list l)
{//proc perm
     int i; int j;
     list tempresult;
     list result;
     if (size(l)==0)
     {
          return(list());
     }
     if (size(l)==1)
     {
          return(list(l));
     }
     for (i = 1; i<=size(l); i++ )
     {
          tempresult = perm(delete(l,i));
          for (j = 1; j<=size(tempresult);j++)
          {
               tempresult[j] = list(l[i])+tempresult[j];
          }
          result = result+tempresult;
     }
     return(result);
}//proc perm

//==================================================
//computes all permutations of a given list by
//ignoring equal entries (faster than perm)
static proc permpp(list l)
{//proc permpp
     int i; int j;
     list tempresult;
     list l_without_double;
     list l_without_double_pos;
     int double_entry;
     list result;
     if (size(l)==0)
     {
          return(list());
     }
     if (size(l)==1)
     {
          return(list(l));
     }
     for (i = 1; i<=size(l);i++)
     {//Filling the list with unique entries
          double_entry = 0;
          for (j = 1; j<=size(l_without_double);j++)
          {
               if (l_without_double[j] == l[i])
               {
                    double_entry = 1;
                    break;
               }
          }
          if (!double_entry)
          {
               l_without_double = l_without_double + list(l[i]);
               l_without_double_pos = l_without_double_pos + list(i);
          }
     }//Filling the list with unique entries
     for (i = 1; i<=size(l_without_double); i++ )
     {
          tempresult = permpp(delete(l,l_without_double_pos[i]));
          for (j = 1; j<=size(tempresult);j++)
          {
               tempresult[j] = list(l_without_double[i])+tempresult[j];
          }
          result = result+tempresult;
     }
     return(result);
}//proc permpp

//==================================================
//factorization of the first Weyl Algebra
proc facwa(poly h)
"USAGE: facwa(h); h is a polynomial in the first Weyl algebra
RETURN: list
PURPOSE: Computes a factorization of a polynomial h in the first Weyl algebra
THEORY: @code{homogfac} returns a list with some factorizations of the given polynomial. The possibilities of the factorization of the highest homogeneous part and those of the lowest will be merged.
EXAMPLE: example facwa; shows examples
SEE ALSO: homogfac_all, homogfac
"{//proc facwa
     if(homogwithorder(h,intvec(-1,1)))
     {
          return(homogfac_all(h));
     }
     //Redefine the ring in my standard form
     if (!isWeyl())
     {//Our basering is not the Weyl algebra
          return(list());
     }//Our basering is not the Weyl algebra
     if(nvars(basering)!=2)
     {//Our basering is the Weyl algebra, but not the first
          return(list());
     }//Our basering is the Weyl algebra, but not the first
     def r = basering;
     map invo = basering,-var(1),var(2);
     int i; int j; int k;
     intvec limits = deg(h,intvec(1,1)) ,deg(h,intvec(1,0)),deg(h,intvec(0,1));
     def prod;
     //end finding the limits
     poly maxh = jet(h,deg(h,intvec(-1,1)),intvec(-1,1))-jet(h,deg(h,intvec(-1,1))-1,intvec(-1,1));
     poly minh = jet(h,deg(h,intvec(1,-1)),intvec(1,-1))-jet(h,deg(h,intvec(1,-1))-1,intvec(1,-1));
     list result;
     list temp;
     list homogtemp;
     list M; list hatM;
     list f1 = homogfac_all(maxh);
     list f2 = homogfac_all(minh);
     int is_equal;
     poly hath;
     for (i = 1; i<=size(f1);i++)
     {//Merge all combinations
          for (j = 1; j<=size(f2); j++)
          {
               M = M + mergence(f1[i],f2[j],limits);
          }
     }//Merge all combinations
     for (i = 1 ; i<= size(M); i++)
     {//filter valid combinations
          if (product(M[i]) == h)
          {//We have one factorization
               result = result + list(M[i]);
               M = delete(M,i);
               continue;
          }//We have one factorization
          else
          {
               if (deg(h,intvec(-1,1))<=deg(h-product(M[i]),intvec(-1,1)))
               {
                    M = delete(M,i);
                    continue;
               }
               if (deg(h,intvec(1,-1))<=deg(h-product(M[i]),intvec(1,-1)))
               {
                    M = delete(M,i);
                    continue;
               }
          }
     }//filter valid combinations
     M = delete_dublicates_eval(M);
     while(size(M)>0)
     {//work on the elements of M
          hatM = list();
          for(i = 1; i<=size(M); i++)
          {//iterate over all elements of M
               hath = h-product(M[i]);
               temp = list();
               //First check for common inhomogeneous factors between hath and h
               if (involution(NF(involution(hath,invo), std(involution(ideal(M[i][1]),invo))),invo)==0)
               {//hath and h have a common factor on the left
                    j = 1;
                    f1 = M[i];
                    if (j+1<=size(f1))
                    {//Checking for more than one common factor
                         while(involution(NF(involution(hath,invo),std(involution(ideal(product(f1[1..(j+1)])),invo))),invo)==0)
                         {
                              if (j+1<size(f1))
                              {
                                   j++;
                              }
                              else
                              {
                                   break;
                              }
                         }
                    }//Checking for more than one common factor
                    f2 = list(f1[1..j])+list(involution(lift(involution(product(f1[1..j]),invo),involution(hath,invo))[1,1],invo));
                    temp = temp + merge_cf(f2,f1,limits);
               }//hath and h have a common factor on the left
               if (reduce(hath, std(ideal(M[i][size(M[i])])))==0)
               {//hath and h have a common factor on the right
                    j = size(M[i]);
                    f1 = M[i];
                    if (j-1>0)
                    {//Checking for more than one factor
                         while(reduce(hath,std(ideal(product(f1[(j-1)..size(f1)]))))==0)
                         {
                              if (j-1>1)
                              {
                                   j--;
                              }
                              else
                              {
                                   break;
                              }
                         }
                    }//Checking for more than one factor
                    f2 = list(lift(product(f1[j..size(f1)]),hath)[1,1])+list(f1[j..size(f1)]);
                    temp = temp + merge_cf(f2,M[i],limits);
               }//hath and h have a common factor on the right
               //and now the homogeneous
               maxh = jet(hath,deg(hath,intvec(-1,1)),intvec(-1,1))-jet(hath,deg(hath,intvec(-1,1))-1,intvec(-1,1));
               minh = jet(hath,deg(hath,intvec(1,-1)),intvec(1,-1))-jet(hath,deg(hath,intvec(1,-1))-1,intvec(1,-1));
               f1 = homogfac_all(maxh);
               f2 = homogfac_all(minh);
               for (j = 1; j<=size(f1);j++)
               {
                    for (k=1; k<=size(f2);k++)
                    {
                         homogtemp = mergence(f1[j],f2[k],limits);
                    }
               }
               for (j = 1; j<= size(homogtemp); j++)
               {
                    temp = temp + mergence(homogtemp[j],M[i],limits);
               }
               for (j = 1; j<=size(temp); j++)
               {//filtering invalid entries in temp
                    if(product(temp[j])==h)
                    {//This is already a result
                         result = result + list(temp[j]);
                         temp = delete(temp,j);
                         continue;
                    }//This is already a result
                    if (deg(hath,intvec(-1,1))<=deg(hath-product(temp[j]),intvec(-1,1)))
                    {
                         temp = delete(temp,j);
                         continue;
                    }
               }//filtering invalid entries in temp
               hatM = hatM + temp;
          }//iterate over all elements of M
          M = hatM;
          for (i = 1; i<=size(M);i++)
          {//checking for complete factorizations
               if (h == product(M[i]))
               {
                    result = result + list(M[i]);
                    M = delete(M,i);
                    continue;
               }
          }//checking for complete factorizations
          M = delete_dublicates_eval(M);
     }//work on the elements of M
     //In the case, that there is none, write a constant factor before the factor of interest.
     for (i = 1 ; i<=size(result);i++)
     {//add a constant factor
          if (deg(result[i][1],intvec(1,1))!=0)
          {
               result[i] = insert(result[i],1);
          }
     }//add a constant factor
     result = delete_dublicates_noteval(result);
     return(result);
}//proc facwa
example
{
     "EXAMPLE:";echo=2;
     ring R = 0,(x,y),Ws(-1,1);
     def r = nc_algebra(1,1);
     setring(r);
     poly h = (x^2*y^2+x)*x;
     facwa(h);
}

//==================================================
/*Singular has no way implemented to test polynomials
 for homogenity with respect to a weight vector.
 The following procedure does exactly this*/
static proc homogwithorder(poly h, intvec weights)
{//proc homogwithorder
     if(size(weights) != nvars(basering))
     {//The user does not know how many variables the current ring has
          return(0);
     }//The user does not know how many variables the current ring has
     int i;
     int dofp = deg(h,weights); //degree of polynomial
     for (i = 1; i<=size(h);i++)
     {
          if (deg(h[i],weights)!=dofp)
          {
               return(0);
          }
     }
     return(1);
}//proc homogwithorder
/*
Example polynomials where one can find factorizations
(x^2+y)*(x^2+y);
(x^2+x)*(x^2+y);
(x^3+x+1)*(x^4+y*x+2);
(x^2*y+y)*(y+x*y);
y^3+x*y^3+2*y^2+2*(x+1)*y^2+y+(x+2)*y; //Example 5 Gregoriev Schwarz.
(y+1)*(y+1)*(y+x*y); //Landau Example projected to the first dimension.
 */