#20436: Bug in solve with option to_poly_solve
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Reporter: bruno | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: symbolics | Keywords: maxima, solve
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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As reported in a [http://ask.sagemath.org/question/33050 question of
ask.sagemath.org], there is a bug when one uses the option `to_poly_solve`
of `solve`:
{{{#!python
sage: p = x^10 - 10*x^8 + 35*x^6 + x^5 - 50*x^4 - 5*x^3 + 25*x^2 + 5*x - 1
sage: p.solve(x, to_poly_solve=True)
Traceback (most recent call last):
...
TypeError: 'sage.symbolic.expression.Expression' object does not support
indexing
}}}
=== Explanation for the bug
The method `solve` with this option rely on Maxima's `to_poly_solve`
function, with option `'algexact:true'`, and expect the follwoing behavior
from Maxima:
* Either return a list of explicit solutions;
* Or raise a `TypeError` (with message containing "Error executing code in
Maxima" or equivalent).
It happens that this is not the case (anymore?):
{{{#!python
sage: (p == 0)._maxima_().to_poly_solve(x, options='algexact:true')
%solve([_SAGE_VAR_x^10-10*_SAGE_VAR_x^8+35*_SAGE_VAR_x^6+_SAGE_VAR_x^5-50*_SAGE_VAR_x^4-5*_SAGE_VAR_x^3+25*_SAGE_VAR_x^2+5*_SAGE_VAR_x-1=0],[_SAGE_VAR_x])
}}}
Since the value returned by Maxima is not in the expected format,
conversion to Sage object fails, as exemplified above.
For completeness, an example where everything works fine follows:
{{{#!python
sage: q = x^6 + x^5 + 3*x^4 + 6*x^3 + x - 1
sage: q.solve(x, to_poly_solve=True)
[x == -1.635043562439497,
x == 0.424403370866086,
x == (0.2765006996266782 - 1.917801305541673*I),
x == (-0.1711805215349513 - 0.595429812852917*I),
x == (-0.1711805215349513 + 0.595429812852917*I),
x == (0.2765006996266782 + 1.917801305541673*I)]
sage: (q == 0)._maxima_().to_poly_solve(x, options='algexact:true')
%union([_SAGE_VAR_x=-1.635043562439497],[_SAGE_VAR_x=0.424403370866086],[_SAGE_VAR_x=0.2765006996266782-1.917801305541673*%i],[_SAGE_VAR_x=-0.595429812852917*%i-0.1711805215349513],[_SAGE_VAR_x=0.595429812852917*%i-0.1711805215349513],[_SAGE_VAR_x=1.917801305541673*%i+0.2765006996266782])
}}}
=== Important note :-)
**I do not know how to fix this bug! **
--
Ticket URL: <http://trac.sagemath.org/ticket/20436>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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