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

• To: mathgroup at smc.vnet.net
• Subject: [mg50019] Re: how to graphically fill the tails of a normal distribution
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 12 Aug 2004 05:43:24 -0400 (EDT)
• Organization: Universitaet Leipzig
• References: <cfcr0h\$46q\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

Needs["Statistics`NormalDistribution`"]
Needs["Graphics`FilledPlot`"]

ndist = NormalDistribution[0, 1];

npdf = PDF[ndist, x]

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

??

Regards
Jens

Todd Allen wrote:
>
> 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 already loaded):
> 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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