On Thursday, November 7, 2013 9:00:36 AM UTC-8, ccandide wrote: > > I dont' understand why Sage is unable to give an exact expression for the > eigenvalues of the following matrix : > > sage: A= matrix([[0,1],[1,-2]]) > sage: [a for a,_,_ in A.eigenvectors_right()] > [-2.414213562373095?, 0.4142135623730951?] >
It does have an exact expression for them. It just prints an approximation to them. The "?" is a bit of a give-away that there might be more to it than just plain floats here: sage: v=[a for a,_,_ in A.eigenvectors_right()][0] sage: parent(v) Algebraic Field sage: v.minpoly() x^2 + 2*x - 1 The reason sage decides to use this representation is because printing these things in terms of sqrt(2) quickly runs out of steam: sage: M=matrix(5,5,[0,1,0,0,0,0,0,1,0,0,0,0,0,1,0,0,0,0,0,1,-3,-1,0,0,0 ]) sage: M.eigenvectors_right()[0][0] -1.132997565885066? (see what you get in maple for that) Perhaps with A=matrix(SR,[[0,1],[1,-2]]) you get an answer that looks more comfortable to you. -- 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 post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/groups/opt_out.
