#12322: invalid simplification of complex logarithm
-------------------------+--------------------------------------------------
Reporter: mjo | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone: sage-5.0
Component: symbolics | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Description changed by mjo:
Old description:
> As pointed out by J.H. Davenport in this sage-support thread,
>
> http://groups.google.com/group/sage-
> support/browse_thread/thread/f9d2209041775c3e
>
> the following (invalid) log simplification is made:
>
> {{{
> sage: t = var('t')
> sage: assume(t, 'complex')
> sage: assumptions()
> [t is complex]
> sage: f = (1/2)*log(2*t) + (1/2)*log(1/t)
> sage: f.full_simplify()
> 1/2*log(2)
> }}}
>
> When, for example, t=-1,
>
> {{{
> sage: f(t = -1)
> I*pi + 1/2*log(2)
> }}}
New description:
As pointed out by J.H. Davenport in this sage-support thread,
http://groups.google.com/group/sage-
support/browse_thread/thread/f9d2209041775c3e
the following (invalid) log simplification is made:
{{{
sage: t = var('t')
sage: assume(t, 'complex')
sage: assumptions()
[t is complex]
sage: f = (1/2)*log(2*t) + (1/2)*log(1/t)
sage: f.full_simplify()
1/2*log(2)
}}}
When, for example, t=-1,
{{{
sage: f(t = -1)
I*pi + 1/2*log(2)
}}}
The assumption that `t` is complex is not necessary here, but simplify
should ''definitely'' not ignore the imaginary part when dealing with
complex functions.
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12322#comment:1>
Sage <http://www.sagemath.org>
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