Calculations with numpy help

[drone626]

I have written code to compute the discriminant of a polynomial f(x) using the determinant of a sylvester matrix which for
f(x)=x^5 -110*x^3 +55*x^2 +2310*x +979 looks like

[[   1    0 -110   55 2310  979    0    0    0]
 [   0    1    0 -110   55 2310  979    0    0]
 [   0    0    1    0 -110   55 2310  979    0]
 [   0    0    0    1    0 -110   55 2310  979]
 [   5    0 -330  110 2310    0    0    0    0]
 [   0    5    0 -330  110 2310    0    0    0]
 [   0    0    5    0 -330  110 2310    0    0]
 [   0    0    0    5    0 -330  110 2310    0]
 [   0    0    0    0    5    0 -330  110 2310]]

Using numpy I simply execute

(-1)**(n*(n-1)/2)(det(a))

where a is the above matrix and n is the degree of f(x). If I don't convert to long python returns 6.31724313067e+17 or 631724313067344384L if I convert.
In either case my result conflicts with maxima which returns 631724313067340625.

I am confident of my code since for polynomials with smaller or sparse coefficient the results agree. For instance if f(x)= x^6 -2, python returns 1492992 as the discriminant and maxima returns 1492992.

Could this be a result of how python handles large integers? I was pretty sure python's large number capabilities were on par. BTW I am running on Arch64 with intel E8400 3.0GHz

Thanks in advance

[Gribouillis]

I don't think numpy supports arbitrary precision computations, so your determinant was probably computed using floating numbers and you have a round off error in the end. There are libraries for arbitrary precision in python, but they usually don't have a determinant function included.