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Re: Exclusions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88115] Re: Exclusions
  • From: m.r at inbox.ru
  • Date: Fri, 25 Apr 2008 05:28:32 -0400 (EDT)
  • References: <fuhqv0$rgt$1@smc.vnet.net> <fuin0b$9le$1@smc.vnet.net>

On Apr 22, 5:30 am, Fiona H Evans <fev... at agric.wa.gov.au> wrote:
> On Apr 22, 2:39 am, Jean-Marc Gulliet <jeanmarc.gull... at gmail.com>
> wrote:
>
> Thanks Jean-Marc,
>
> My first post here - I have discovered the limitations of copying and
> pasting. In my notebook, the syntax is correct.
>
> I don't expect an automatic exclusion, but I do get an additional
> (unwanted) exclusion at y==0 && x<0 when I use the following command:
>
> Plot3D[ pdfN[{x, y}], {x, -3, 3}, {y, -3, 3}, PlotRange -> Full,
>  Mesh -> 30,  ColorFunction -> grayColors, PlotPoints -> 50,
>  ClippingStyle -> None,
>  Exclusions -> { {ArcTan[x, y] == 0.5,
>     x > 0 && y > 0}, {ArcTan[x, y] == -Pi + 0.5, x < 0 && y < 0}},=

>  ExclusionsStyle -> {None, Directive[Thick, Red]}, MaxRecursion -> 0,
>  AxesLabel -> {"x", "y"}]
>
> Regards, Fiona.

Exclusion search effectively works by bracketing the root, so when you
have ArcTan jump from -Pi to Pi it will also count as a root, similar
to FindRoot[x - Round[x], {x, .25, .75}]. You can try adding a
condition that excludes the unwanted region:

Plot3D[Arg[((x + I y) E^(-.5 I))], {x, -1, 1}, {y, -1, 1},
 Exclusions -> {{Arg[x + I y] == -Pi + 0.5,
    Abs@ Arg[x + I y] < Pi - .25}},
 ExclusionsStyle -> {None, Red},
 Method -> {"RotationControl" -> "ArcBall"}]

Maxim Rytin
m.r at inbox.ru


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