Comment #6 on issue 1724 by asmeurer: conjugate doesn't work for rational powers http://code.google.com/p/sympy/issues/detail?id=1724
I don't think we should return a numeric solution when we are looking for a symbolic one. If the symbolic one can't be found, I think we should raise. If that is not enough for the user, then he can then resort to numeric methods. If you look at the source, we are evaluating the conjugate of a power as conjugate(x**y) == conjugate(x)**y. But I think this only holds when y is an integer (which is why it is screwing up on these rational powers that don't have I explicitly in them). I don't know if this is the best way or even if it would work in general, but it seems that maybe this could be a method to solve issue 216 and hence this one using the fact that roots returns nicer expressions: In [14]: a = S("(-29/54 + 93**(1/2)/18)**(1/3)") In [15]: a.evalf() Out[15]: 0.0542694215230746 + 0.0939973953753372⋅ⅈ In [16]: a Out[16]: ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽ ╱ ⎽⎽⎽⎽ ╱ 29 ╲╱ 93 3 ╱ - ── + ────── ╲╱ 54 18 In [17]: roots(x**3 - a**3, x).keys() Out[17]: ⎡ ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽ ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽ ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽ ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎤ ⎢ ╱ ⎽⎽⎽⎽ ╱ ⎽⎽⎽⎽ ╱ ⎽⎽⎽⎽ ╱ ⎽⎽⎽⎽ ⎥ ⎢ ╱ 29 ╲╱ 93 ⎽⎽⎽ ╱ 29 ╲╱ 93 ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽ ╱ 29 ╲╱ 93 ⎽⎽⎽ ╱ 29 ╲╱ 93 ⎥ ⎢3 ╱ ── - ────── ⅈ⋅╲╱ 3 ⋅3 ╱ ── - ────── ╱ ⎽⎽⎽⎽ 3 ╱ ── - ────── ⅈ⋅╲╱ 3 ⋅3 ╱ ── - ────── ⎥ ⎢╲╱ 54 18 ╲╱ 54 18 ╱ 29 ╲╱ 93 ╲╱ 54 18 ╲╱ 54 18 ⎥ ⎢────────────────── - ──────────────────────────, -3 ╱ ── - ────── , ────────────────── + ──────────────────────────⎥ ⎣ 2 2 ╲╱ 54 18 2 2 ⎦ In [18]: map(N, roots(x**3 - a**3, x).keys()) Out[18]: [0.0542694215230746 - 0.0939973953753372⋅ⅈ, -0.108538843046149, 0.0542694215230746 + 0.0939973953753372⋅ⅈ] -- You received this message because you are listed in the owner or CC fields of this issue, or because you starred this issue. You may adjust your issue notification preferences at: http://code.google.com/hosting/settings -- You received this message because you are subscribed to the Google Groups "sympy-issues" group. To post to this group, send email to sympy-iss...@googlegroups.com. To unsubscribe from this group, send email to sympy-issues+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy-issues?hl=en.