#10133: Make sure log(1) returns an Integer, not an int
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Reporter: kcrisman | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone: sage-4.6.1
Component: symbolics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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From [http://groups.google.com/group/sage-
devel/browse_thread/thread/cceabb7271022b1c/944c94af910269a0 this thread]:
{{{
> > sage: type(log(1))
> > <type 'int'>
> > sage: log(1).n()
> >
---------------------------------------------------------------------------
> > AttributeError: 'int' object has no attribute 'n'
> > sage: Integer(log(1)).n()
> > 0.000000000000000
> > sage: a = Integer(1)
> > sage: a.log()
> > 0
> > sage: type(a.log())
> > <type 'int'>
> > sage: from sage.functions.log import function_log
> > sage: function_log(Integer(1))
> > 0
> > sage: type(function_log(Integer(1)))
> > <type 'int'>
>
> > Is there any way to get around this in the code, or are we pretty much
> > stuck with this because of how GinacFunctions work? I'm not 100% sure
> > this is a bug in log; maybe instead we should extend int so that
>
> This is a bug in the log() function, and any other function which
> returns exact values like 0 or 1. We already work around most cases,
> see lines 720-722 and 736-761 of sage/symbolic/function.pyx.
>
> The correct fix is to change the corresponding pynac functions to
> coerce the exact value to the parent of the argument before returning
> it. For example, all the lines "return _ex1;" or "return _ex0;" in
>
> http://pynac.sagemath.org/hg/file/b233d9dadcfa/ginac/inifcns_trans.cpp
>
> has to be changed this way.
>
Yup, I see what you are talking about - e.g.
if (x.is_equal(_ex1)) // log(1) -> 0
return _ex0;
Although it might be nice to stay relatively close to Ginac and fix such
things on the Sage level if that's not really bad.
}}}
This ticket's goal is to implement one of these solutions (that is, catch
this in function.pyx or in Pynac).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10133>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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