Issue with equations of irreducible components of semistable model

[shiva-chid]

The following code computes the irreducible components of the semistable model of a curve C. The first irreducible component has an equation u1^2 = sextic, but sage returns 0 for its genus. The equation returned for the second irreducible component has three variables in it: u1, u2, x; and sage returns -1 for its genus.

sage: from mclf import *
sage: R.<x> = QQ[]
sage: C = SuperellipticCurve(x^6 + 8*x^5 - 8*x^4 + 22*x^3 - 8*x^2 + 8*x + 1,2)
sage: vp = QQ.valuation(101)
sage: Cp = SemistableModel(C,vp)
sage: Cp.components()
[the smooth projective curve with Function field in u1 defined by u1^2 + 100*x^6 + 93*x^5 + 8*x^4 + 79*x^3 + 8*x^2 + 93*x + 100,
 the smooth projective curve with Function field in u2 defined by u2^2 + 20*u1*x^2 + 92*u1 + 78]
sage: [x.genus() for x in Cp.components()]
[0, -1]

[saraedum]

@swewers do you understand what's the issue here?

[oossen]

I can't reproduce this! Using the newest version of mclf, I get genera [0, 0] (and this does have reduction genus 2, so is the proper semistable reduction). Using an older version from before Issue #124, I get an error similar to the one I posted there.

[saraedum]

@shiva-chid could you clarify which versions of SageMath and related packages you are using?

[saraedum]

To install the latest (unreleased) version of mclf, you could use pip install git+https://github.com/mclf/mclf. Does the problem still exist with that version of mclf?

[shiva-chid]

I am running Sage 9.4. I still seem to get the same result after installing mclf 1.0.4.

[shiva-chid]

sage: pip install git+https://github.com/mclf/mclf                              
Defaulting to user installation because normal site-packages is not writeable
Collecting git+https://github.com/mclf/mclf
  Cloning https://github.com/mclf/mclf to /tmp/pip-req-build-vohet911
  Running command git clone -q https://github.com/mclf/mclf /tmp/pip-req-build-vohet911
Requirement already satisfied: patchy in ./.sage/local/lib/python3.9/site-packages (from mclf==1.0.4) (2.5.0)
WARNING: You are using pip version 21.1.2; however, version 22.0.4 is available.
You should consider upgrading via the '/home/sage/sage-9.4/local/bin/python3 -m pip install --upgrade pip' command.
Note: you may need to restart the kernel to use updated packages.
sage: from mclf import * 
....: R.<x> = QQ[] 
....: C = SuperellipticCurve(x^6 + 8*x^5 - 8*x^4 + 22*x^3 - 8*x^2 + 8*x + 1,2) 
....: vp = QQ.valuation(101) 
....: Cp = SemistableModel(C,vp) 
....: [x.genus() for x in Cp.components()] 
....:                                                                           
[0, -1]

[saraedum]

It works for me. I used SageMath 9.5 as distributed by conda-forge:

$ micromamba create -n deleteme sage=9.5 pip
$ micromamba activate deleteme
$ pip install git+https://github.com/mclf/mclf
$ sage
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 9.5, Release Date: 2022-01-30                     │
│ Using Python 3.10.2. Type "help()" for help.                       │
└────────────────────────────────────────────────────────────────────┘
sage: sage: from mclf import *
....: ....: R.<x> = QQ[]
....: ....: C = SuperellipticCurve(x^6 + 8*x^5 - 8*x^4 + 22*x^3 - 8*x^2 + 8*x + 1,2)
....: ....: vp = QQ.valuation(101)
....: ....: Cp = SemistableModel(C,vp)
....: ....: [x.genus() for x in Cp.components()]
[0, 0]