#10761: Numerical approximation of an algebraic number raises a ValueError
----------------------------+-----------------------------------------------
Reporter: slabbe | Owner: tbd
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7
Component: numerical | Keywords: numerical_approx, AlgebraicNumber
Author: Simon Spicer | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
----------------------------+-----------------------------------------------
Changes (by newvalueoldvalue):
* keywords: => numerical_approx, AlgebraicNumber
* status: new => needs_review
* component: PLEASE CHANGE => numerical
* author: => Simon Spicer
Comment:
The patch provides a short and sweet fix to the above problem. The issue
arises in sage/misc/functional.py's numerical_approx() function:
{{{
if not (is_ComplexNumber(x) or is_ComplexDoubleElement(x)):
try:
return sage.rings.real_mpfr.RealField(prec)(x)
except TypeError:
pass
return sage.rings.complex_field.ComplexField(prec)(x)
}}}
Attempting to call RealField() on a complex AlgebraicNumber raises a
ValueError and not a TypeError, so the exception is not caught. Changing
the except clause to catch all errors fixes this:
{{{
if not (is_ComplexNumber(x) or is_ComplexDoubleElement(x)):
try:
return sage.rings.real_mpfr.RealField(prec)(x)
# Trac 10761: now catches all errors (instead of just
# a TypeError), since calling RealField on AlgebraicNumbers
# can raise a ValueError
except:
pass
return sage.rings.complex_field.ComplexField(prec)(x)
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10761#comment:1>
Sage <http://www.sagemath.org>
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