Igor Schein on Tue, 1 Dec 1998 14:16:02 -0500 |
[Date Prev] [Date Next] [Thread Prev] [Thread Next] [Date Index] [Thread Index]
nfdisc() performance |
Hi, after Karim's latest patch fixed nfdisc(x^18+16) problem, I looked into other polynomials of form x^18+n. It turned out nfdisc is extremely slow for n=(9*m)^2, where n is NOT a cube of an integer ( if n is a cube, then x^18+n is reducible ). The first few *bad* polynomials are: x^18+81 (m=1) x^18+324 (m=2) x^18+1296 (m=4) x^18+2025 (m=5) etc. I looked at the \g output, it deals with polynomials with huge coefficients in the process, but I don't really know the algorithm to make an educated guess. I was wondering if it's a short-coming of the algorithm and can be improved, or it's expected and cannot be improved. Thanks Igor P.S. BTW, I use this little hack to check whether the integer is a cube: iscube(n)=vecmax(Vec(factor(n))[2]%3)==0 \\ n>1 Is there a better way in GP to do that?