Re: how to graphically fill the tails of a normal distribution

• To: mathgroup at smc.vnet.net
• Subject: [mg50039] Re: [mg50012] how to graphically fill the tails of a normal distribution
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Thu, 12 Aug 2004 05:44:12 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Needs["Graphics`"];

Needs["Statistics`NormalDistribution`"];

ndist=NormalDistribution[0, 1];

npdf=PDF[ndist,x];

FilledPlot[npdf{1,UnitStep[x+2]-UnitStep[x-2]},
{x,-4,4},Fills->Red, PlotRange->All];

FilledPlot[npdf{1,If[Abs[x]<2,1,0]},
{x,-4,4},Fills->Red, PlotRange->All];

FilledPlot[npdf{1,If[-2<x<2,1,0]},
{x,-4,4},Fills->Red, PlotRange->All];

Bob Hanlon

>
> From: Todd Allen <genesplicer28 at yahoo.com>
To: mathgroup at smc.vnet.net
> Date: 2004/08/11 Wed AM 05:53:11 EDT
> To: mathgroup at smc.vnet.net
> Subject: [mg50039] [mg50012] how to graphically fill the tails of a normal distribution
>
>
> Hello all,
>
>       Hope you don't mind a question from a biologist trying to learn
Mathematica.  I have been teaching myself the syntax of Mathematica to
analyze microarray data (i.e, a technology to simultaneously monitor the
expression levels of thousands of genes).  I am interested in producing a plot
for a presentation in which the tails of a normal distribution are colored red
to illustrate a concept.  I can get the plot to work with a single tail, but I can't
get the syntax to work for both tails of the disribution.  Here is my code:
>
> This works for a single tail, with the following code (necessary packages
> ndist=NormalDistribution[0,1]
>
> npdf=PDF[ndist,x]
>
> FilledPlot[{npdf,If[x³2,0,npdf]},{x,-4,4},Fills®RGBColor[1,0,0]]
>
> However when I try the following with the Or operator (at least I think Or
operator):
>
> FilledPlot[{npdf,If[x³2.0þx£-2.0,0,npdf]},{x,-4,4},Fills®RGBColor[1,0,0]]
>
> I get a series of error messages:
>
> Plot:plnr:If[x³2.0þx£-2.0,0,npdf] is not a machine-size real number at x=
-4
>
> This error repeats itself with different x values and then a normal curve is
drawn with neither tail colored in.
>
>
>
> What am I missing here?
>
> Any insight is much appreciated, thanks!
> Todd
>

```

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