## #315 closed bug (fixed)

# identical rows of syzygies over the Weyl algebra

Reported by: | Owned by: | somebody | |
---|---|---|---|

Priority: | minor | Milestone: | 3-1-3 and higher |

Component: | dontKnow | Version: | 3-1-2 |

Keywords: | Cc: |

### Description

the syz command for the Weyl algebra produces a highly redundant matrix with many *identical* columns of syzygies

LIB "nctools.lib";
ring A=0,(z,x,y,dz,dx,dy),dp;
def S=Weyl();
setring S;
matrix m[1][6] = x^{2*y}8+2*x*y^{9+y}10+2*x^{5*y}4+2*x^{4*y}5+x^{8,-z*x*y}8-z*y^{9-5*z*x}4*y^{4-4*z*x}3*y^{5-4*z*x}7,z^{2*y}8+8*z^{2*x}3*y^{4+z*y}8+16*z^{2*x}6-4*z*x^{3*y}4-12*z*x^{2*y}5+4*z*x^{6,4*z}2*x*y^{7+5*z}2*y^{8+16*z}2*x^{4*y}3+20*z^{2*x}3*y^{4+z*y}8+12*z*x^{4*y}3+20*z*x^{3*y}4,-4*z*x^{2*y}7-9*z*x*y^{8-5*z*y}9-4*z*x^{5*y}3-5*z*x^{4*y}4,16*z^{2*x}2*y^{6+40*z}2*x*y^{7+25*z}2*y^{8+4*z*x}2*y^{6+8*z*x*y}7+5*z*y^{8-12*z*x}5*y^{2-20*z*x}4*y^{3;
matrix s=syz(m);
s[3]==s[2];
s[3]==s[4];
s[3]==s[5];
s[3]==s[6];
s[3]==s[7];
s[3]==s[8];
}

### Change History (3)

### comment:1 Changed 12 years ago by

Resolution: | → fixed |
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Status: | new → closed |

### comment:2 Changed 12 years ago by

Can't look at the code at the moment, but one has to make sure that what one deletes is
a **left** multiple of what remains; per default we work with left modules...
Regards,
Viktor

### comment:3 Changed 12 years ago by

idDelMultiples deletes polys which differ by a factor in the ground field.

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In principle: this is correct, but not good: it shows that we need more/better criteria for the PLURAL case. fixed with the help of idDelMultiples