Re: plot error messages are completelly missing

*To*: mathgroup at smc.vnet.net*Subject*: [mg81038] Re: plot error messages are completelly missing*From*: Helen Read <read at math.uvm.edu>*Date*: Sat, 8 Sep 2007 03:59:19 -0400 (EDT)*References*: <fbojp5$jbs$1@smc.vnet.net> <fbqqoe$7c5$1@smc.vnet.net>

Szabolcs wrote: > Josef Otta wrote: >> Hi all, >> >> I have a question to a catching error messages is the evaluation of >> graphics functions in the version 6. For example, consider a function >> plotting with non real values: >> >> {Plot[Sqrt[x], {x, -2, 1}], >> $MessageList} >> >> in version 5.2 the output is a plot with these messages >> >> {Plot::plnr, Plot::plnr, Plot::plnr, General::stop}} >> >> If I use the same approach in the version 6.0 i get no error messages >> and that is a big problem for me. Do you have any idea how to get >> these errors? >> I do not know how to get these messages also in the cases where >> >> Complex, ComplexInfinity, Indeterminate, Null, Underflow or Overflow >> >> occur in the evaluation of almost every graphics function. > > I would like to know this too. On[General::plnr] turns on this warning > message. However, the message is only issued when Plot encounters a > symbolic expression. It does not work for complex numbers, infinity etc. > > And I do not understand why this new General::plnr is turned off by > default. Passing a completely non-numerical argument (as opposed to a > function that evaluates to complexes in some regions) to Plot is an > unintentional mistake in 99% of the cases. The only time I turned off > Plot::plnr in 5.2 was when repeatedly plotting things like Plot[Sqrt[x], > {x, -1, 1}], but these kinds of examples do not warn with Plot::plnr any > more in Mathematica 6 (even though it would often be useful). I for one am glad that I no longer see those annoying "not a machine size real number" messages. It's no longer a problem to plot a function across an interval where it is not real. For example, I can now plot ArcSec[x] for {x,-5,5} and get a nice looking plot, or plot Sqrt[x] together with Sqrt[x+5] on {x,-5,5} without having to plot them separately and Show. To me this is an improvement. On a somewhat related topic, I really like the new Exclusions option. -- Helen Read University of Vermont