#11941: Solve and assumptions too aggressive with cube root of negative numbers
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Reporter: kcrisman | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone: sage-4.7.3
Component: symbolics | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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#6515 did a great job helping us start to catch some assumptions when we
do solving.
However, [http://ask.sagemath.org/question/824/real-solution-of-x38-0 this
ask.sagemath.org post] catches a case where it's too aggressive, because
Sage says that `(-1)^(1/3)` is not real.
{{{
sage: solve(x^3+1==0,x)
[x == 1/2*I*(-1)^(1/3)*sqrt(3) - 1/2*(-1)^(1/3), x ==
-1/2*I*(-1)^(1/3)*sqrt(3) - 1/2*(-1)^(1/3), x == (-1)^(1/3)]
sage: assume(x,'real')
sage: solve(x^3+1==0,x)
[]
}}}
What's weird about this is that the Maxima in Sage should just return
`x==-1`.
{{{
(%i2) display2d:false;
(%o2) false
(%i3) solve(x^3+1=0,x);
(%o3) [x = -(sqrt(3)*%i-1)/2,x = (sqrt(3)*%i+1)/2,x = -1]
}}}
Not sure what's going on with that.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11941>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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