Re: Plot bug?

*To*: mathgroup at smc.vnet.net*Subject*: [mg6365] [mg6365] Re: [mg6354] Plot bug?*From*: Richard Gass <gass at physics.uc.edu>*Date*: Fri, 14 Mar 1997 14:53:45 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Brad Miller wrote >Hi, > 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 PopRatio[pratio_]:= 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 physunc.uc.edu