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Re: plot error messages are completelly missing

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  • Subject: [mg81038] Re: plot error messages are completelly missing
  • From: Helen Read <read at>
  • Date: Sun, 9 Sep 2007 06:09:39 -0400 (EDT)
  • References: <fbojp5$jbs$> <fbqqoe$7c5$>

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

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