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7.7.3.0. SannfsBFCT
Procedure from library dmod.lib (see dmod_lib).

Usage:
SannfsBFCT(f [,eng]); f a poly, eng an optional int

Return:
ring

Purpose:
compute Ann f^s and Groebner basis of Ann f^s+f in D[s]

Note:
activate the output ring with the setring command.
This procedure, unlike SannfsBM, returns a ring with the degrevlex
ordering in all variables.
In the ring D[s], the ideal LD is the ideal needed (which is returned as a Groebner basis).
If eng <>0, std is used for Groebner basis computations,
otherwise, and by default slimgb is used.

Display:
If printlevel=1, progress debug messages will be printed,
if printlevel>=2, all the debug messages will be printed.

Example:
 
LIB "dmod.lib";
ring r = 0,(x,y,z,w),Dp;
poly F = x^3+y^3+z^3*w;
printlevel = 0;
def A = SannfsBFCT(F); setring A;
intvec v = 1,2,3,4,5,6,7,8;
// are there polynomials, depending on @s only?
nselect(LD,v);
==> _[1]=27*@s^6+252*@s^5+960*@s^4+1910*@s^3+2093*@s^2+1198*@s+280
// a fancier example:
def R = reiffen(4,5); setring R;
v = 1,2,3,4;
RC; // the Reiffen curve in 4,5
==> xy4+y5+x4
def B = SannfsBFCT(RC);
setring B;
// Are there polynomials, depending on @s only?
nselect(LD,v);
==> _[1]=0
// It is not the case. Are there leading terms in @s only?
nselect(lead(LD),v);
==> _[1]=63750000000000000000*@s^7


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