On Sun, Jan 10, 2010 at 10:07 PM, cfriedalek <[email protected]> wrote:
> OK I'm just a casual user trying to get the roots of a sequence of
> polynomials. Thought I'd report a bug. I have pythonxy 2.6.2 installed
> which comes with Sympy 0.6.5. In that version the roots failed at X**4
> as in:
>
> import sympy
> x = sympy.Symbol('x')
>
> PASS
> sympy.roots(x**2 + x -5, x)
> sympy.roots(x**3 + x**2 + x - 7, x)
>
> FAIL - returns and empty dictionary
> sympy.roots(x**4 + x**3 + x**2 + x - 9, x)
>
>
> I checked the sympy site and saw a reference to solve fixes so I
> installed 0.6.6. With that version the x**4 polynomial root passes.
Yes, this was fixed in 0.6.6.
> However the next polynomial in the sequence fails i.e.
> sympy.roots(x**5 + x**4 + x**3 + x**2 + x - 11, x)
> {}
>
> A simple numerical root finder gives one real root.
As far as I know there is no symbolical algorithm to determine roots
of polynomials of 5th order.
E.g. even wolfram alpha gives just numerical roots:
http://www.wolframalpha.com/input/?i=roots+of+x**5+%2B+x**4+%2B+x**3+%2B+x**2+%2B+x+-+11
>
> Can't see this being user error but as a casual user it could be. Hope
> this helps you fix a bug.
Thanks for reporting it. How do you imagine the fix ---- there seems
to be no algorithm to return a symbolic root. So you would expect
roots() to automatically return numeric roots?
Ondrej
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