Let's start with the expression expr = -2.61468835142518e-12*I*x**3 - 1.77367468147515e-13*x**2 + 2.01551297295763e-14*I*x + 6.13636683162216e-92*1/x**2 - 1.320867768074e-41* I*1/x + 7.79634921616583e-16
It is not a polynomial in x, because it contains negative powers of x. If you force it to be a polynomial with poly(expr), it becomes a polynomial with respect to x and 1/x. And that is a multivariate polynomial (x and 1/x are like two variables). Hence the error: nroots does not work with multivariate polynomials. Instead, get rid of the negative powers of x first. For example, numer, denom = factor(expr).as_numer_denom() which returns numerator and denominator as a tuple, (-2.61468835142518e-12*I*x**5 - 1.77367468147515e-13*x**4 + 2.01551297295763e-14*I*x**3 + 7.79634921616583e-16*x**2 - 1.320867768074e-41 *I*x + 6.13636683162216e-92, x**2) (The factoring is optional, but helpful in order to get a simpler numerator-denominator split). Now, the roots of the original expression are the roots of the numerator, except any that are shared with the denominator. Now we can convert the numerator to a polynomial and use nroots: p = poly(numer, x) p.nroots() Output: [0, 0, -0.0808688047608342 + 0.0115783613847529*I, 0.0446783092911365*I, 0.0808688047608342 + 0.0115783613847529*I] which is disappointing because 0 is obviously not a root of the numerator. The tiny size of constant term is a problem, it creates some roots that are too close to 0 for double-precision computations to discern. We need more precision (parameter n), which in turn requires more iterative steps (parameter maxsteps). p.nroots(n=50, maxsteps=200) This looks better: [-0.080868804760834166180018845175030947090976577924994 + 0.011578361384752871275300055197605686713645998543873*I, - 4.6457086620940071146527033337243530690040397643132e-51*I, 1.6942131906240984280655485817471796195769008732488e-26*I, 0.044678309291136464439409743198239609092604642312342*I, 0.080868804760834166180018845175030947090976577924994 + 0.011578361384752871275300055197605686713645998543873*I] On Monday, February 26, 2018 at 8:42:55 AM UTC-5, k wrote: > > Hi > I am trying to understand how to simplify a Polynomial in Sympy without > any 1/x or 1/x^n terms. > > Because solving for roots, the domain won't work with nroots. > > The error I get. > > MultivariatePolynomialError: can't compute numerical roots of > Poly(-2.61468835142518e-12*I*x**3 - ' > 1.77367468147515e-13*x**2 + 2.01551297295763e-14*I*x + > 6.13636683162216e-92*1/x**2 - 1.320867768074e-41*I*1/x + > 7.79634921616583e-16, x, 1/x, domain='EX') > > Any help would be of great assistance. > > -- 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 sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/213a8ff9-93d0-45c0-96b9-f62d5d0d89a8%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
