You evaluate it over ZZ[x1,...,xn] rather than GF(2)[x1,...,x4]. Anyways, it simply can't be *that* slow in any case: even: the (theoretically ) maximum number of monoms that can be in any expansion is less than a few thousands, so the upper limit for a naively implemented Gaussian elimination is in the order of seconds. However the matrix is even much simpler than that and even the inverse is computed immediately.
On 12/17/09, [email protected] <[email protected]> wrote: > And another observation: > > maxima returns answer immediatelly (with a lag necessary to start > maxima) > m is the original matrix from x.py > > sage: m._maxima_().determinant().expand().sage() > x0^2*x2^2*x3^2*x7^2 - 2*x0*x1*x2*x3*x4*x5*x6*x7 + x1^2*x4^2*x5^2*x6^2 > > > Anyway, the answer is different from expected one. I do not konw which > one is correct. > > Robert > > > > On 17 pro, 11:40, "[email protected]" <[email protected]> wrote: > > perhaps problems expanding polynomials? even determinant of submatrix > > (0,0,5,5) is suprisingly slow. > > > > workaroud is to replace polynomials in your matrix by variables. > > > > var('x0 x1 x2 x3 x4 x5 x6 x7 a1 a2 a3 a4 a5 a6 a7 b1 b2 b3 b4 b5 b6 > > b7') > > m=matrix([[ 0, a1, a2, a3, a4, a5, a6, a7], > > [b1, 0, x0, 0, 0, 0, 0, 0], > > [b2, x0, 0, x6, 0, 0, 0, 0], > > [b3, 0, x6, 0, x3, 0, 0, 0], > > [b4, 0, 0, x3, 0, x4, 0, 0], > > [b5, 0, 0, 0, x4, 0, x2, 0], > > [b6, 0, 0, 0, 0, x2, 0, x1], > > [b7, 0, 0, 0, 0, 0, x1, 0]]) > > m > > > > m.det() gives answer immediatelly and you can substitute back for a's > > and b's. > > > > > -- > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org > -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
