Singular NULL pointer with a ring of the form QQ(t)[x, y]/(f)

[pjbruin]

(Duplicate of #12188)

The following returns the right thing in the end, but exhibits a problem with calling Singular in the process:

sage: K.<t> = FunctionField(QQ)
sage: A.<x,y> = PolynomialRing(K, 2)
sage: B = A.quotient(y^2 + (t + 1)*x*y + t*y - x^3 - t*x^2)
sage: B.gens()
verbose 0 (3490: multi_polynomial_ideal.py, groebner_basis) Warning: falling back to very slow toy implementation.
singular_ring_delete(ring*) called with NULL pointer.
  File "/home/staff/pbruin/src/sage-5.11.beta3/local/bin/sage-ipython", line 18, in <module>
    app.start()
...
  File "/home/staff/pbruin/src/sage-5.11.beta3/local/lib/python2.7/site-packages/sage/rings/polynomial/multi_polynomial_ideal.py", line 910, in _groebner_strategy
    return GroebnerStrategy(MPolynomialIdeal(self.ring(), self.groebner_basis()))
Exception KeyError: (The ring pointer 0x0,) in 'sage.libs.singular.ring.singular_ring_delete' ignored
(xbar, ybar)

Probably Gröbner bases shouldn't even be invoked in this example, but that is another question.

Component: commutative algebra

Keywords: Singular NULL pointer

Reviewer: Jeroen Demeyer, Peter Bruin, Volker Braun

Issue created by migration from https://trac.sagemath.org/ticket/14902

[jdemeyer]

comment:1

Looks very much like #12188.

[kcrisman]

comment:2

Volker says that this ask.sagemath question is a duplicate as well.

[pjbruin]

Description changed:

--- 
+++ 
@@ -1,3 +1,5 @@
+(Duplicate of #12188)
+
 The following returns the right thing in the end, but exhibits a problem with calling Singular in the process:

[pjbruin]

comment:3

I posted a patch for #12188 that fixes this ticket as well. Now the output of the above example is

verbose 0 (3490: multi_polynomial_ideal.py, groebner_basis) Warning: falling back to very slow toy implementation.
(xbar, ybar)

[vbraun]

Reviewer: Volker Braun

[vbraun]

Author: Peter Bruin

[vbraun]

comment:4

I agree, same issue as #12188.

[jdemeyer]

Changed author from Peter Bruin to none

[jdemeyer]

Changed reviewer from Volker Braun to Jeroen Demeyer, Peter Bruin, Volker Braun