Opened 14 years ago

Closed 14 years ago

## #257 closed bug (duplicate)

# example lift over Q(t): bad perfomance / hung machine

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

Priority: | minor | Milestone: | 3-1-2 and higher |

Component: | singular-kernel | Version: | 3-1-1 |

Keywords: | lift rational function field | Cc: |

### Description

This was a forum entry from September 22, 2008; no problem for Magma but bad perf. in SINGULAR resp. hung machine:

ring R = (0,t), (w,x,y,z), dp;
poly f = w^{3 + x}3 + y^{3 + z}3 + t*((w+x)*(w+2*y)*(w+3*z) + 3*x*y*(w+x+z));
ideal jac = jacob(f);
print(lift(jac, x^{4));
}

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Magma V2.16-11 gives normal form (plus coefficients for GB elements to arrive at this normal form) immediately:

Q<s> := PolynomialRing?(Rationals()); F<t> := FieldOfFractions?(Q);

R := PolynomialRing?(F, 4, "grevlex"); AssignNames?(~R, ["w", "x", "y", "z"]); w := R.1; x := R.2; y := R.3; z := R.4;

f := w

^{3 + x}3 + y^{3 + z}3 + t*((w+x)*(w+2*y)*(w+3*z) + 3*x*y*(w+x+z)); jac := JacobianIdeal?(f); j := GroebnerBasis?(jac);n, C := NormalForm?(x

^{4, j); }n; C;