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MathGroup Archive 2006

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Re: Simplification and Arg[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66599] Re: Simplification and Arg[]
  • From: "Jaccard Florian" <Florian.Jaccard at he-arc.ch>
  • Date: Mon, 22 May 2006 18:14:30 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

hello!

I must admit it is difficult to guess...

ComplexExpand[Arg[a + b*I], TargetFunctions ->

{Re, Im}]

gives ArcTan[a, b]

ComplexExpand[Arg[1 + I*x] + Arg[1 - I*x],

TargetFunctions -> {Re, Im}]

gives  0

Regards

F.Jaccard




________________________________

De: Andrew Moylan [mailto:andrew.moylan at anu.edu.au]
=C0: mathgroup at smc.vnet.net
Objet : [heur] [mg66593] Simplification and Arg[]



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?

Cheers,

Andrew

P.S. Apologies if I have sent this twice; my original message seems not
to have worked.




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