Re: Simplification and Arg[]
- To: mathgroup at smc.vnet.net
- Subject: [mg66604] Re: Simplification and Arg[]
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Mon, 22 May 2006 18:14:40 -0400 (EDT)
- Organization: The University of Western Australia
- References: <e4r7qm$mmh$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <e4r7qm$mmh$1 at smc.vnet.net>,
Andrew Moylan <andrew.moylan at anu.edu.au> wrote:
> Should Mathematica be able to simplify the following expression? (It is
> easily seen to be zero under the given condition, x > 0.)
>
> FullSimplify[
> Arg[1 + I * x] + Arg[1 - I * x],
> {x > 0}
> ]
>
> In particular, I would have expected the following to yield ArcTan[b /
> a], from which the above expression is easily reduced to zero:
>
> FullSimplify[
> Arg[a + I b],
> {a > 0, b > 0}
> ]
>
> Any ideas?
I would use ComplexExpand instead of FullSimplify:
ComplexExpand[Arg[I*x + 1] + Arg[1 - I*x], TargetFunctions -> {Re, Im}]
0
ComplexExpand[Arg[a + I b], TargetFunctions -> {Re, Im}]
ArcTan[a, b]
Cheers,
Paul
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