Opened 5 years ago

Last modified 4 years ago

## #16848 new defect

# solve of ideal over QQ[x,y] does not give solution anymore (since 6.3)

Reported by: | dkrenn | Owned by: | |
---|---|---|---|

Priority: | major | Milestone: | |

Component: | algebra | Keywords: | |

Cc: | Merged in: | ||

Authors: | Reviewers: | ||

Report Upstream: | N/A | Work issues: | |

Branch: | Commit: | ||

Dependencies: | Stopgaps: |

### Description

In Sage 6.3 we have

sage: R.<x,y> = QQ[] sage: I = R.ideal(y^2 - 2*y + 1, x + 1/4*y - 5/4) sage: solve(I.gens(), [SR(x) for x in R.gens()], solution_dict=true) []

But in 6.1.1 we got

sage: solve(I.gens(), [SR(x) for x in R.gens()], solution_dict=true) [{x: 1, y: 1}]

which was the correct solution.

### Change History (4)

### comment:1 Changed 5 years ago by

### comment:2 Changed 5 years ago by

Hi,

I would not say this is a bug. If you want to use the function `solve`

, you need to feed it with symbolic polynomials

sage: R.<x,y> = QQ[] sage: Sx, Sy = var('x,y') sage: I = R.ideal(y^2 - 2*y + 1, x + 1/4*y - 5/4) sage: f0,f1 = I.gens() sage: f0 = f0.subs(x=Sx, y=Sy); f1 = f1.subs(x=Sx, y=Sy) sage: solve([f0,f1], [Sx,Sy], solution_dict=true) [{x: 1, y: 1}]

The "bug" comes from `solve`

which does not type check the input as it should. Note that when the input is one polynomial the check is done

sage: f0,f1 = I.gens() sage: solve(f0, [Sx,Sy]) Traceback (most recent call last): ... TypeError: The first argument must be a symbolic expression or a list of symbolic expressions.

Vincent

### comment:3 follow-up: ↓ 4 Changed 4 years ago by

See also #13360 automatically coercing from polynomials to symbolics can cause unexpected problems. So, while I acknowledge that this ugly and unconvenient I am more inclined to get used to write

sage: R.<x,y> = QQ[] sage: I = R.ideal(y^2 - 2*y + 1, x + 1/4*y - 5/4) sage: solve(map(SR,I.gens()), map(SR,R.gens()), solution_dict=true) [{y: 1, x: 1}]

### comment:4 in reply to: ↑ 3 Changed 4 years ago by

Replying to lftabera:

See also #13360 automatically coercing from polynomials to symbolics can cause unexpected problems. So, while I acknowledge that this ugly and unconvenient I am more inclined to get used to write

sage: R.<x,y> = QQ[] sage: I = R.ideal(y^2 - 2*y + 1, x + 1/4*y - 5/4) sage: solve(map(SR,I.gens()), map(SR,R.gens()), solution_dict=true) [{y: 1, x: 1}]

Ok, this is definitly a workaround and maybe should be mentioned somewhere. Anyhow, I do not like that solve as in the original problem accepts polynomials but then does not give a solution (while it did some versions ago)

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I've narrowed the search: It works in 6.3.beta5, but not anymore in 6.3.beta6.