quotient of ideals throws up Singular bug

[mariah]

This is a bug in Singular 3.1.7 (fixed in 4.0.1, see ticket #17254):

R.<xe,xv> = ZZ[]

J = Ideal(4*xv^3+3*xv^2, 3*xe*xv^2+xe-2*xv);

I  = Ideal(-3, -3*xv-1, -3);
I2 = Ideal(-3, -3*xv-1);
assert( I  == I2 )

Q1 = J.quotient(I) # wrong
Q2 = J.quotient(I2)

assert( Q1 == Q2 ) # fails

[jakobkroeker]

This bug (and some others) are fixed in recent ​Singular:

ring rng = integer,(x,y,z),dp;
ideal A = x^2, x*y, x*z;
ideal B = x;
quotient(A,B);
//_[1]=z
//_[2]=y
//_[3]=x

(offtopic: are all known Singular-bugs reported ​upstream? )

However, I recall that there are some issues when considering updating Singular :

• there is no stable/official release yet
• in sage-devel (?, cannot currently find the post I had in mind) it was mentioned that the libSingular interface changed significantly in comparison to v 3.1.6

[jakobkroeker]

the bug above is fixed by upgrade to Singular 3.1.7

but there is at least another one (fixed in 4.0.1, see ticket #17254):

R.<xe,xv> = ZZ[]

J = Ideal(4*xv^3+3*xv^2, 3*xe*xv^2+xe-2*xv);

I  = Ideal(-3, -3*xv-1, -3);
I2 = Ideal(-3, -3*xv-1);
assert( I  == I2 )

Q1 = J.quotient(I) # wrong
Q2 = J.quotient(I2)


assert( Q1 == Q2 ) # fails

[gh-mwageringel]

Since the bug is fixed, here is a branch removing the stopgap warning and adding the example from the description as a doctest.

(Ignore the pyflakes warning for now. I will deal with it on another ticket, as the unused macaulay2 variable should actually be used.)

---

New commits:

​873857a

12803: remove stopgap and add doctest

[klee]

LGTM