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Re: Redefine Arg to return a value from 0 to 2 pi
*To*: mathgroup at smc.vnet.net
*Subject*: [mg80463] Re: Redefine Arg to return a value from 0 to 2 pi
*From*: dh <dh at metrohm.ch>
*Date*: Thu, 23 Aug 2007 01:03:24 -0400 (EDT)
*References*: <faeash$f5i$1@smc.vnet.net>
Hi Chuck,
it is bad practise to redefine built in funcions, you may run into
troubles you did not anticipate. I think it is better to write your own
version, what can be done e.g. by
myArg[x_]:=Mod[Arg[x],2Pi]
hope this helps, Daniel
chuck009 wrote:
> I'm trying to redefine Arg to return a value from 0 to 2 pi. However when I do so and then try and plot Arg[z], Mathematica seems to still use the old definition. Can anybody help me? This is my code:
>
> (* redefine Arg to return a value from 0 to 2 pi *)
>
> Unprotect[Arg]
> Arg[z_] := Module[{z0 = z}, If[Im[z0] < 0,
> ArcTan[Re[z0], Im[z0]] + 2*Pi, ArcTan[Re[z0],
> Im[z0]]]];
> Protect[Arg]
>
> (* check new definition -- this is correct *)
>
> ListPlot[Table[{t, Arg[2*Exp[I*t]]}, {t, 0, 4*Pi, 0.1}]]
>
> (* try and plot new definition of Arg -- Plot used the old definition (-pi to pi) *)
>
> Plot[Arg[2*Exp[I*t]], {t, 0, 4*Pi}]
>
> (* resore old definition of Arg *)
>
> Unprotect[Arg]
> Arg[z_] =.
> Protect[Arg]
>
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