Re: weibull plot on weibull scaled paper

*To*: mathgroup at smc.vnet.net*Subject*: [mg116722] Re: weibull plot on weibull scaled paper*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Fri, 25 Feb 2011 06:34:42 -0500 (EST)

You're probably right. Bobby On Thu, 24 Feb 2011 05:21:14 -0600, Darren Glosemeyer <darreng at wolfram.com> wrote: > On 2/23/2011 4:24 AM, Bill Rowe wrote: >> On 2/22/11 at 1:12 PM, btreat1 at austin.rr.com (DrMajorBob) wrote: >> >>> This gave the FindRoot:jsing error on the first try just now... and >>> also the third try. >>> dist = WeibullDistribution[7, 200]; >>> data = RandomVariate[dist, 300]; >>> ProbabilityScalePlot[data, "Weibull"] >>> QuantilePlot[data, dist] >>> So the error is not unusual. >> Hmmm... If I copy and paste just >> >> dist = WeibullDistribution[7, 200]; >> data = RandomVariate[dist, 300]; >> ProbabilityScalePlot[data, "Weibull"] >> >> into a single cell then execute it, I see the error you >> reported. Alternatively, if I type the above by hand into a >> single cell I still see the error you reported consistently. Or >> I can copy each line one by one pasting each into a cell then >> execute each line before pasting the next and still get the error. >> >> But if I enter each line by hand into individual cells, I don't >> see the error. So, there appears to be a bug somewhere. That is, >> the various ways I've described above of doing the computation >> should all behave identically. >> >> > > ProbabilityScalePlot and its friends call the internal parameter > estimation code for FindDistributionParameters/EstimatedDistribution to > get the estimates. The reason for the message is that the equations in > the estimation code for WeibullDistribution were less numerically stable > than they could have been and so convergence fails more often than it > should when parameter values are somewhat large. This has been fixed for > the next release. > > I think the fact that the example worked without error when you typed > the inputs in separate cells is a red herring. The example will converge > for some data sets and not for others. I suspect the random values you > got in the case that worked just happened to give a convergent result > while the random values you'd gotten in the other attempts did not. > > Darren Glosemeyer > Wolfram Research > -- DrMajorBob at yahoo.com