#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-4.8
Component: symbolics | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by mboratko):
I've attached a fairly limited workaround, but it does give (semi?)
desirable behavior:
{{{
sage: assume(x, 'real')
sage: solve(x^3+1==0,x)
[x == (-1)^(1/3)]
}}}
If it is then up to the user to interpret the result, this seems ok. If
they want to programmatically use the result later, it's really no good. I
suppose if they were aware of this and wanted to fix the result to be real
then they could manually employ the same method as in my patch to the
result.
I guess, as a more general question, do we want the results of solve to
always return a result with domain: real, and if so can we make this
change for just this function? If there is a use case where this is
undesirable, then I think the only option is make the assumptions file not
only check the returned value, but also modify it (so that if assume is
real, then the value is actually replaced with the real values). Perhaps
another option is to allow the user to specify the desired domain of
results from solve.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11941#comment:9>
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