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D.15.21.4 MSGB

Procedure from library stdmodule.lib (see stdmodule_lib).

Usage:
MSGB(G,A); G submodule over subalgebra A, A subalgebra (which is a finite sagbi basis).

Return:
a module MB: standard bases of G over subalgebra A."

Example:
 
LIB "stdmodule.lib";
// Example 1:
ring r=ZZ,(x,y),Dp;
ideal A=2x2+xy,2y2,3xy;
ideal I=4x2y2+2xy3,18x2y4;
MSGB(I,A);
==> _[1]=4x2y2*gen(1)+2xy3*gen(1)
==> _[2]=18x2y4*gen(1)
// Example 2:
ring r2=QQ,(x,y),Dp;
ideal A= x2-xy+y, y2+x;
module G=x2y2-xy3+x3-x2y+y3+x2+y, y4+2xy2+x2-y2-x;
MSGB(G,A);
==> _[1]=x2y2*gen(1)-xy3*gen(1)+x3*gen(1)-x2y*gen(1)+y3*gen(1)+x2*gen(1)+y*ge\
   n(1)
==> _[2]=y4*gen(1)+2xy2*gen(1)+x2*gen(1)-y2*gen(1)-x*gen(1)
==> _[3]=2x2*gen(1)-2xy*gen(1)+2y*gen(1)
// Example 3:
ring r3=QQ,(x,y,z),Dp;
ideal A= x3-yz+2x, x2y2+xz2+3z;
module G=[x3-yz+2x, x2y2+xz2+3z, 2],[x2y2-x3+xz2+yz-2x-3z, 2x3-2yz+4x, -x2y2-xz2-3z+3],[x6-2x3yz+4x4+y2z2-4xyz+4x2, x6y6+3x5y4z2+3x4y2z4+9x4y4z+x3z6+18x3y2z3+x5y2+9x2z5+27x2y2z2+27xz4+27z3, x5y2+x4z2-x2y3z+2x3y2-xyz3+3x3z+2x2z2-3yz2+6xz];
MSGB(G,A);
==> _[1]=x2y2*gen(2)+x3*gen(1)+xz2*gen(2)-yz*gen(1)+2x*gen(1)+3z*gen(2)+2*gen\
   (3)
==> _[2]=-x2y2*gen(3)+x2y2*gen(1)+2x3*gen(2)-x3*gen(1)-xz2*gen(3)+xz2*gen(1)-\
   2yz*gen(2)+yz*gen(1)+4x*gen(2)-2x*gen(1)-3z*gen(3)-3z*gen(1)+3*gen(3)
==> _[3]=x6y6*gen(2)+3x5y4z2*gen(2)+3x4y2z4*gen(2)+9x4y4z*gen(2)+x3z6*gen(2)+\
   18x3y2z3*gen(2)+x5y2*gen(3)+x5y2*gen(2)+9x2z5*gen(2)+x6*gen(1)+x4z2*gen(3\
   )-x2y3z*gen(3)+27x2y2z2*gen(2)+2x3y2*gen(3)-2x3yz*gen(1)-xyz3*gen(3)+27xz\
   4*gen(2)+4x4*gen(1)+3x3z*gen(3)+2x2z2*gen(3)+y2z2*gen(1)-4xyz*gen(1)-3yz2\
   *gen(3)+27z3*gen(2)+4x2*gen(1)+6xz*gen(3)
==> _[4]=x7y4*gen(1)+2x6y2z2*gen(1)-x4y5z*gen(1)+2x5y4*gen(1)+x5z4*gen(1)-2x3\
   y3z3*gen(1)+6x5y2z*gen(1)+2x4y4*gen(3)+4x4y2z2*gen(1)-x2yz5*gen(1)-x5y2*g\
   en(3)-x5y2*gen(2)+6x4z3*gen(1)+4x3y2z2*gen(3)+2x3z4*gen(1)-6x2y3z2*gen(1)\
   -x6*gen(1)-x4z2*gen(3)+12x3y2z*gen(1)+x2y3z*gen(3)+2x2z4*gen(3)-6xyz4*gen\
   (1)-2x3y2*gen(3)+2x3yz*gen(1)+9x3z2*gen(1)+12x2y2z*gen(3)+12x2z3*gen(1)+x\
   yz3*gen(3)-4x4*gen(1)-3x3z*gen(3)-x2y2*gen(3)+x2y2*gen(1)-2x2z2*gen(3)+12\
   xz3*gen(3)-y2z2*gen(1)-9yz3*gen(1)+2x3*gen(2)-x3*gen(1)+4xyz*gen(1)-xz2*g\
   en(3)+19xz2*gen(1)+3yz2*gen(3)-4x2*gen(1)-6xz*gen(3)-2yz*gen(2)+yz*gen(1)\
   +18z2*gen(3)+4x*gen(2)-2x*gen(1)-3z*gen(3)-3z*gen(1)+3*gen(3)

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