#11941: Solve and assumptions too aggressive with cube root of negative numbers
-------------------------+--------------------------------------------------
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:
-------------------------+--------------------------------------------------
Changes (by mboratko):
* milestone: => sage-4.8
Comment:
The fact that Maxima normally returns -1 and Sage returns (-1)^(1/3) is a
bit odd, as you mentioned. At a more basic level, Sage doesn't seem to
think that (-1)^(1/3) is in RR:
{{{
sage: (-1)^(1/3) in RR
False
sage: (2)^(1/3) in RR
True
}}}
So if we fix that problem, then at least it would return (-1)^(1/3). I
also suspect that it would properly simplify to -1 at that point as well,
based on the following example:
{{{
sage: solve(x^3-8==0,x)
[x == I*sqrt(3) - 1, x == -I*sqrt(3) - 1, x == 2]
sage: solve(x^3+8==0,x)
[x == I*(-1)^(1/3)*sqrt(3) - (-1)^(1/3), x == -I*(-1)^(1/3)*sqrt(3) -
(-1)^(1/3), x == 2*(-1)^(1/3)]
}}}
(Note that the (1/3) exponent appears everywhere next to the -1, as if
some rule specifies that sage should not simplify it out.)
I am new, however, and I am not sure where next to look.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11941#comment:2>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en.
