Exclusions

• To: mathgroup at smc.vnet.net
• Subject: [mg87978] Exclusions
• From: Fiona H Evans <fevans at agric.wa.gov.au>
• Date: Mon, 21 Apr 2008 06:39:44 -0400 (EDT)

```I'm having a little trouble with the use of "Exclusions" for plotting.

If I use "Exclusions -> Automatic" in the following, Plot3D finds no
exclusions.

pdfN[{x_, y_} := PDF[MultinormalDistribution[{0, 0}, {{1, 0}, {0,
1}}], {x, y}];

grayColors = Function[{x, y, z}, (Lighter[Gray, #] &)[z]];

Plot3D[ pdfN[{x, y}], {x, -3, 3}, {y, -3, 3}, PlotRange -> Full,
Mesh -> 30,  ColorFunction -> grayColors, PlotPoints -> 50,
Exclusions -> Automatic,
ExclusionsStyle -> {None, Directive[Thick, Red]}, MaxRecursion -> 0,
AxesLabel -> {"x", "y"}]

However, if I try to exclude a cross-section through the mean of the
distribution asin the following, as well as my defined Exclusions, I
get an exclusion drawn at {y == 0, x < 0}, even though I have used
inequalities to exclude y == 0 from my Exclusions.

Plot3D[ pdfN[{x, y}], {x, -3, 3}, {y, -3, 3}, PlotRange -> Full,
Mesh -> 30,  ColorFunction -> grayColors, PlotPoints -> 50,
Exclusions -> {{ArcTan[x, y] == 0.5, x > 0 && y > 0}, {ArcTan[x, y]
== -Pi + 0.5, x < 0 &7 y < 0}},
ExclusionsStyle -> {None, Directive[Thick, Red]}, MaxRecursion -> 0,
AxesLabel -> "x", "y"}]

Can anyone see a way that I can avoid this?

Regards, Fiona.

```

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