#3829: [with patch, positive review] wester.py disagrees with Wester!!!
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Reporter: rlm | Owner: gfurnish
Type: defect | Status: new
Priority: major | Milestone: sage-3.4.1
Component: symbolics | Resolution:
Keywords: |
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Comment (by rlm):
Replying to [comment:8 fredrik.johansson]:
> Why should this be considered true? The equality clearly doesn't hold
for all x. Try for example evaluating numerically with x = 3.
>
> Or is some nonstandard branch cut convention implied here?
Fredrik,
I spent quite some time convincing myself that that identity is true. The
proof is attached as PDF. You must be able to take the logarithm of
`tan(x/2 + pi/4)` in order for the identity to make sense, but for any
branch you take where it makes sense it is true. The problem with
evaluating numerically at `x = 3` is that symbolic log doesn't like
negative numbers, and `tan(3/2 + pi/4) = -1.15265520898227` so it returns
a `NaN`.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/3829#comment:9>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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