On Wed, Sep 22, 2021 at 9:19 AM Dima Pasechnik <dimp...@gmail.com> wrote:
> > > On Wed, Sep 22, 2021 at 8:10 AM Tracy Hall <h.tr...@gmail.com> wrote: > >> I ran into an assertion error when trying to return a sorted list whose >> key was a certain linear combination of eigenvalues of the Laplacian matrix >> over graphs on nine vertices. Digging into it a bit, the failure happened >> when comparing an algebraic real number against the same number that was >> constructed differently (starting with the graph complement). Digging >> further, the error happens when finding roots of a certain degree 56 >> polynomial over AA (all the roots are real) but there is no error doing the >> same thing over QQbar. >> >> Here is a minimal working example: >> >> P.<z> = QQ[] >> rootlist = (z^8 - 32*z^7 + 425*z^6 - 3044*z^5 + 12789*z^4 - 32090*z^3 + >> 46672*z^2 - 35734*z + 10917).roots(AA) >> problem = rootlist[-1][0] - rootlist[0][0] - 9 >> >> problem.minpoly().roots(AA) >> > > indeed, problem.minpoly().roots(QQbar) produces a list of 56 QQbar > elements, more precisely, pairs (t,1)), each t convertible into AA. > One funny discrepancy is that one of the elements of this list is shown as > (-6.390396068452545? + 0.?e-170*I, 1) > > sage: rrr=problem.minpoly().roots(QQbar) > sage: rrr[-1] > (-6.390396068452545? + 0.?e-170*I, 1) > sage: AA(rrr[-1][0]) > -6.390396068452545? > > Not sure whether this is the cause of the bug, though. > The behaviour of QQbar is not very consistent there. Only one root is shown with an imaginary part, but the polynomial has integer coefficients --- it ought to "know" that complex roots come in pairs :-) > Dima > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-support/CAAWYfq35Omovg-jPnG6a3eKLLa%2BpaL-%3D%3DCRFpgPRasn%2BwBf8qA%40mail.gmail.com.
