On Wed, Sep 22, 2021 at 8:10 AM Tracy Hall <[email protected]> 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. Dima -- You received this message because you are subscribed to the Google Groups "sage-nt" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-nt/CAAWYfq2ix_U_S5DxM6kC-pDUCbx5KEGFFxobKgaSNE_FupRGvg%40mail.gmail.com.
