On Fri, Jan 14, 2011 at 5:03 PM, Michel Talon <talon at lpthe.jussieu.fr>wrote:
> Edwin Woollett wrote:
>
> > Maxima by Example, Ch. 12, Dirac Algebra
> > and Quantum Electrodynamics update Jan. 10, 2011.
>
> Hi, Edwin
>
> i have just looked at your manuals, and noted a problem i remarked
> recently,
> that you may have not noted in your Chapter 9, use of bfallroots.
>
> The problem is that if you feed a polynomial with bfloat coefficients (*)
> to bfallroots, to get the solution, the first thing it does is to convert
> all coeffs to rats, and does that with small precision (something like
> eight digits), so you can set fpprec=30 as much as you want the solutions
> are not correct to more than 7 digits.
>
>
Oops. I guess that's also a bug in allroots. I think allroots and
bfallroots should bind ratepsilon to the same precision of fpprec. Or maybe
not rat the polynomial at all.
Don't know if you do this, but if you define your bfloat polynomial with a
value of fpprec, and then change it to a different value before calling
bfallroots, the accuracy might be a bit different from what you expected
because the original coefficients have the original fpprec precision.
Ray