MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Simplification and Arg[]


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

_______________________________________________________________________
Paul Abbott                                      Phone:  61 8 6488 2734
School of Physics, M013                            Fax: +61 8 6488 1014
The University of Western Australia         (CRICOS Provider No 00126G)    
AUSTRALIA                               http://physics.uwa.edu.au/~paul


  • Prev by Date: Graphics--ProgressBar in GUIKit
  • Next by Date: Re: Simplification and Arg[]
  • Previous by thread: Re: Simplification and Arg[]
  • Next by thread: Re: Simplification and Arg[]