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MathGroup Archive 1997

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Re: Plot bug?

  • To: mathgroup at
  • Subject: [mg6365] [mg6365] Re: [mg6354] Plot bug?
  • From: Richard Gass <gass at>
  • Date: Fri, 14 Mar 1997 14:53:45 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Brad Miller wrote
>	I am running the new version of mathematica (3.0), and some
>code that worked under the old version (2.x?) is not working.
>pseudo-mathematica session
>1> Needs["Statistics`ContinuousDistributions`"]
>2> PopRatio[pratio_]:=
>	Module[{p}, p=CDF[NormalDistribution[0,1],pratio];
>	- 2 pratio / Ln[(1-p)/p]
>	]
>3> Plot[PopRatio[x],{x,.000001,.7}]
>Errors: "Plot::plnr : PopRatio[pratio] is not a machine-size real
>           number at pratio = 0.0283978535340494791"
>  and many other points also say not a machine-size real number
>Doing a PopRatio[0.0283978535340494791] on the reported bad number
>produces the correct PopRatio return value - it does not blow up.  So,
>I'm surmising the problem is in the Plot cmd?
>This exact fn worked in mathematica 2.x - result should be a plot from
>around 1.26 to 1.2 - there are no discontinuities in the plot.
>Any suggestions on how to get PopRatio to plot correctly?

The problem is the use of Ln for the natural log. Mathematica uses Log. If
you change Ln to Log and try
	Module[{p}, p=CDF[NormalDistribution[0,1],pratio];
	- 2 pratio / Log[(1-p)/p]
the function will work correctly.

Richard Gass
Department of Physics
University of Cincinnati
Cincinnati, OH 45221
phone- 513-556-0519
E-Mail gass at

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