yoda789's profile - activity

Thanks for this code. This solution also works for me !

Thanks ! This command works but it doesn't give the list of roots, unlike the code of Emmanuel Charpentier.

Thank you very much ! The numerical resolution works perfectly ! But notice that you have forgotten "t^4" term in F definition. Then, the solving of the equation give 6 roots

{-2.8752155238395045 - 1.6035277768266649e-16*I,
 -0.5433030528116871 + 2.5081428804803407e-17*I,
 0.5277361688701939 - 0.5071712949223567*I,
 0.5277361688701941 + 0.5071712949223569*I,
 0.9541487172225926 + 1.4813528249977233e-16*I,
 1.408897521688212 + 3.3107296343907337e-16*I}

which are identical to the ones given by Mathematica.

{{x -> -2.87522},{x -> -0.543303},{x -> 0.527736-0.507171i},{x -> 0.527736+0.507171i},{x -> 0.95415},{x -> 1.4089}}

This suits me.

However, for information, I would to mention that I've checked the following code on https://sagecell.sagemath.org/ :

P.<t>=PolynomialRing(CDF);
FF=FractionField(P);
alpha=[CDF(complex(2*(random()-0.5),2*(random()-0.5))) for p in range(6)];

F=alpha[1]+alpha[2]*t+alpha[3]*t^2+t^4+(alpha[4]+alpha[5]*t^2)/(t^2-alpha[0]);

foo=SR(repr(F).replace("t","x")).solve(x)
[q.rhs().n() for q in foo]

and I've got the following errors :

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-a2132da36519> in <module>()
     19 
     20 foo=SR(repr(F).replace("t","x")).solve(x)
---> 21 [q.rhs().n() for q in foo]
     22 

/home/sc_serv/sage/src/sage/structure/element.pyx in sage.structure.element.Element.n (build/cythonized/sage/structure/element.c:8063)()
    861             0.666666666666667
    862         """
--> 863         return self.numerical_approx(prec, digits, algorithm)
    864 
    865     N = deprecated_function_alias(13055, n)

/home/sc_serv/sage/src/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression.numerical_approx (build/cythonized/sage/symbolic/expression.cpp:36129)()
   5782             res = x.pyobject()
   5783         else:
-> 5784             raise TypeError("cannot evaluate symbolic expression numerically")
   5785 
   5786         # Important -- the  we get might not be a valid output for numerical_approx in

TypeError: cannot evaluate symbolic expression numerically

Hi !

I was used to solve the following equation with Mathematica. \begin{equation} \alpha_1 + \alpha_2x + \alpha_3x^2 + x^4 + \frac{\alpha_4}{x^2-\alpha_0} + \frac{\alpha_5 x^2}{x^2-\alpha_0}=0 \end{equation} where $\alpha_i$ are constants.

The Mathematica function "Solve" gives me all the numerical roots of this non polynomial equation very easily. These roots can be real or complex.

I'm a very beginner at Sage. I have tried several methods to solve this equation automatically but it seems that all methods I've used work only for polynomial equations. Here they are :

alpha0 = 0.25
alpha1 = -2.5
alpha2 = 6.9282
alpha3 = -5.5
alpha4 = 0.5
alpha5 = -0.5
x = var('x')
eq = alpha1 + alpha2*x + alpha3*x**2 + x**4 + alpha4/(x**2 - alpha0) + alpha5*x**2/(x**2 - alpha0) == 0.

# test 1
# solve(eq, x, ring=CC)
# ==> [0 == 20000*x^6 - 115000*x^4 + 138564*x^3 - 32500*x^2 - 34641*x + 22500]

# test 2
# solve(eq, x, ring=CC, solution_dict=True)
# ==> [{0: 20000*x^6 - 115000*x^4 + 138564*x^3 - 32500*x^2 - 34641*x + 22500}]

# test 3
# eq.roots(x, ring=CC,multiplicities=False)
# ==> TypeError: fraction must have unit denominator

Do you have any idea of a method to get the approximated roots of the equation ?

Thanks in advance

EDIT : correction of an error in the equation ; add few tests