[sage-support] Re: Spurious numerical solutions of polynomial equation

2013-12-14 Thread JamesHDavenport
Sorry - I was looking at the original *(I*x^51+sum(x^k,k,0,50))==0.* Note that if you make the x->x-1 substitution, the polynomial now has coefficient as large as 10^18. The discriminant is unchanged, but the value you would expect it to be, given the size of the coefficient, is roughly10^800 t

[sage-support] Re: Spurious numerical solutions of polynomial equation

2013-12-14 Thread Volker Braun
Apparently you need about 65 bits of accuracy, presumably maxima uses doubles (=53 bits). Compare: sage: eq = (I*x^51+sum(x^k,k,0,50)).subs(x=x-1-I) sage: var('x, k') (x, k) sage: eq = (I*x^51+sum(x^k,k,0,50)).subs(x=x-1-I) sage: sol = eq.polynomial(ComplexField(65)).roots() sage: [abs(eq.subs(x=

[sage-support] Re: Spurious numerical solutions of polynomial equation

2013-12-14 Thread JamesHDavenport
Curious. The polynomial does not seem particularly ill-conditioned, in the sense that its discriminat is roughly what one might expect (unlike, say, Wilkinson's). Maple gives 50 roots with |f(x)|<10^{-12}, and one with f(x)=, i.e. much larger. On Thursday, 12 December 2013 15:35:53 UTC, AWWQUB