Opened 6 years ago

Closed 5 years ago

# Missing (?) final std (redSB) in primdec

Reported by: Owned by: gorzel somebody minor 4-2-0 and higher singular-libs 4-1-0 primdecGTZ (radical)

### Description

Why does primdec not peforms a final std on the radical components? It does not cost too much to do this, but it will often clearify the result.

Example, the solution is just the point x=2,y=2:

```> LIB "primdec.lib";
> ring r =0,(x,y),dp;
> ideal I = y^4-8*y^3+24*y^2-32*y+16,
. 1/32*y^3-15/64*y^2+x+1/8*y-25/16;

_[1]=y-2
_[2]=x-2

> primdecGTZ(I);
[1]:
[1]:
_[1]=y4-8y3+24y2-32y+16
_[2]=1/32y3-15/64y2+x+1/8y-25/16
[2]:
_[1]=y-2
_[2]=1/32y3-15/64y2+x+1/8y-25/16
> option(redSB);
> primdecGTZ(I);
[1]:
[1]:
_[1]=y4-8y3+24y2-32y+16
_[2]=1/32y3-15/64y2+x+1/8y-25/16
[2]:
_[1]=y-2
_[2]=1/32y3-15/64y2+x+1/8y-25/16    // <-- simplify this !
> ideal J = _[1][2];
> std(J);
_[1]=y-2
_[2]=x-2
```

Compare:

```> facstd(I);
[1]:
_[1]=-128xy+65y2+64x+80y-36
_[2]=1024x2-259y2-2752x+448y+1548
_[3]=2y3-15y2+64x+8y-100
> primdecSY(I);
[1]:
[1]:
_[1]=128xy-65y2-64x-80y+36
_[2]=1024x2-259y2-2752x+448y+1548
_[3]=2y3-15y2+64x+8y-100
[2]:
_[1]=y-2
_[2]=x-2
```

### comment:1 Changed 6 years ago by hannes

std/groebner is a costly operation and should only be used if required.

### comment:2 Changed 5 years ago by hannes

Resolution: → wontfix new → closed
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