Updates:
Summary: spurious imaginary component durint evalf (was "subs or N has an
issue with quartic/quadratic root")
Comment #11 on issue 2362 by [email protected]: spurious imaginary component
durint evalf (was "subs or N has an issue with quartic/quadratic root")
http://code.google.com/p/sympy/issues/detail?id=2362
Note: there are no longer 4 roots given for this equation with the Euler
quartic method in place:
solve(u**4 - 3*u + 4)
[sqrt(8/(3*(9/16 + sqrt(42591)*I/144)**(1/3)) + 2*(9/16 +
sqrt(42591)*I/144)**(1
/3))/2 - sqrt(-2*(9/16 + sqrt(42591)*I/144)**(1/3) + 6/sqrt(8/(3*(9/16 +
sqrt(42
591)*I/144)**(1/3)) + 2*(9/16 + sqrt(42591)*I/144)**(1/3)) - 8/(3*(9/16 +
sqrt(4
2591)*I/144)**(1/3)))/2, sqrt(-2*(9/16 + sqrt(42591)*I/144)**(1/3) +
6/sqrt(8/(3
*(9/16 + sqrt(42591)*I/144)**(1/3)) + 2*(9/16 + sqrt(42591)*I/144)**(1/3))
- 8/(
3*(9/16 + sqrt(42591)*I/144)**(1/3)))/2 + sqrt(8/(3*(9/16 +
sqrt(42591)*I/144)**
(1/3)) + 2*(9/16 + sqrt(42591)*I/144)**(1/3))/2]
[(u**4 - 3*u + 4).subs(u,r).n() for r in _]
[0.e-132 - 0.e-132*I, 0.e-133 + 0.e-132*I]
But there is still the evalf problem.
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