Hi Mario, Thank you for the reply.
`solutions = [s.expand(complex=True) for s in solutions]` worked for me, now `im()` and `is_real()` return the correct results. Of course the solutions were correct, the problem was with `im()` and `is_real()` not being able to calculate the correct results. May be they should be modified to simplify (in this case, expand) the inputs before doing anything else? Regards, Thilina. On Wed, Sep 11, 2013 at 5:02 PM, mario <[email protected]> wrote: > The solutions are correct but the real solution is not written in a > simple form > > > >>> solutions = solve(2*x**3 - 3*x**2 - 3*x - 1) > >>> solutions[1].n() > 2.26116669667966 - 0.e-23*I > >>> solutions = [s.expand(complex=True) for s in solutions] > >>> solutions[1] > 1/2 + 3**(1/3)/2 + 3**(2/3)/2 > > > > On Wednesday, September 11, 2013 12:36:56 PM UTC+2, Thilina Rathnayake > wrote: >> >> Hi All, >> >> I am trying to implement the solutions for cubic Thue equation and to do >> that >> I have to solve cubic equations. I use `solve()` to do this. But I am >> having a little >> trouble filtering out real solutions from the solution list returned by >> `solve()`. >> >> I tried the following. >> >> In [5]: from sympy.abc import x >>> In [6]: solutions = solve(2*x**3 - 3*x**2 - 3*x - 1) >>> >> In [8]: for s in solutions: >>> ...: print(sympify(s).is_real) >>> ...: >>> None >>> None >>> None >>> >> >> But one of the solutions in this equation is real. See below: >> http://www.wolframalpha.com/**input/?i=2*x**3+-+3*x**2+-+3***x+-+1<http://www.wolframalpha.com/input/?i=2*x**3+-+3*x**2+-+3*x+-+1> >> >> That is also included in the list returned by `solve()` >> >> In [9]: solutions[0] >>> Out[9]: 1/2 - (-3)**(1/3)/2 + (-3)**(2/3)/2 >>> >> >> But, Interestingly, >> >> In [10]: for s in solutions: >>> ....: print(im(s)) >>> ....: >>> -3**(5/6)/4 + 3*3**(1/6)/4 >>> im((-3)**(2/3)/(-1/2 + sqrt(3)*I/2))/2 - im((-3)**(1/3)*(-1/2 + >>> sqrt(3)*I/2))/2 >>> im((-3)**(2/3)/(-1/2 - sqrt(3)*I/2))/2 - im((-3)**(1/3)*(-1/2 - >>> sqrt(3)*I/2))/2 >>> >> >> `im()` of `solutions[0]` should be zero. Am I doing something wrong here >> or is this a bug? >> Are there any other methods to find whether a number is purely real or >> not? >> >> Thank you in advance. >> >> Regards, >> Thilina. >> >> -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
