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 _______________________________________________________________________ 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