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Re: Stop on message?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126692] Re: Stop on message?
  • From: Szabolcs HorvÃt <szhorvat at gmail.com>
  • Date: Thu, 31 May 2012 02:49:18 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201205260911.FAA07083@smc.vnet.net> <jpspa5$hb9$1@smc.vnet.net>

Hello Christoph,

I think it all comes down to whether you are writing a self-contained
GUI application or you're writing a function.

The only GUI application I wrote was an image uploader:

http://meta.mathematica.stackexchange.com/questions/5/can-i-easily-post-images-to-this-site-directly-from-mathematica-yes

It does issue messages (to the console) when things go wrong, but I'll
be ready to admit that these are more of an annoyance than useful for
the end user.  The only reason I left them in is so that I can
diagnose and fix problems more easily (people can tell me about the
messages when something went wrong).

On 30 May 2012 09:48, Christoph Lhotka <christoph.lhotka at fundp.ac.be> wrote:
> Hello,
>
> thank you for your detailed answer. The two examples
> you mention are in good agreement with my argumentation:
>
> A message marks an error or a warning and should
> be taken as a motivation to change the code until
> those messages disappear:
>
> Example 1:
>
>
> Solve[-26.81 == 194 k + k*l*32.9 && 22.2 == -74 k + k*l*59.7, {k,l}]
>
> The "error" is that one uses a function which is designed to
> return an exact solution for an inexact equation. The solution to
> the "message problem" is not (!) to wrap Quiet[] around the code
> but to use the right function for the right purpose, which in that
> case is NSolve:
>
> NSolve[-26.81 == 194 k + k*l*32.9 && 22.2 == -74 k + k*l*59.7, {k, l}]
>
> No message is generated any more.
>
>
> Example 2:
>
>
> FindMinimum[x^2/2 + Cos[x], {x, 1}]
>
> The essential part of the message, which is returned is the sentence:
>
> "...The line search decreased the step size to within the tolerance
> specified by AccuracyGoal and PrecisionGoal but was unable to find a
> sufficient decrease in the function...."
>
> Which just tells us that the function FindMinimum was unable to do the job,
> so the result is questionable. Fortunately, Mathematica gives you a hint how
> to deal with the issue:
>
> FindMinimum[x^2/2 + Cos[x], {x, 1}, WorkingPrecision -> 24]
>
> Again, no warning message is produced.
>
>
> I think, that in my over 10 years of Mathematica experience I always took
> the right choice to 1) be sure that any function I used or developed does
> not produce a warning message before 2) I use them to implement another
> function on their basis.
>
> I also agree that the discussion maybe unessential for the interactive user.
>
> Best,
>
> Christoph
>
>
>
> On 05/29/2012 06:22 PM, Szabolcs Horv=C3=A1t wrote:
>>
>> Hi Christoph,
>>
>> Mathematica is used interactive most of the time. =C2 It's very different
>> from most other programming languages in this respect. =C2 In C, or even
>> in Python (which has an interactive shell), most of the time people 1.
>> first write the program and debug it 2. then they package it up and
>> give it to the user to run. =C2 In Mathematica we typically don't write
>> stand-alone programs. =C2 The system is usually used interactive, and the
>> most "packaged up" things are functions meant to be used by end-users.
>> =C2 In other words: even the user is a programmer.
>>
>> When you make a standalone program like a text editor, your users
>> shouldn't see any internal warnings/errors (on Linux these messages
>> are often printed to the console on they're pretty uninformative to
>> me, as a user, 95% of the time). =C2 When you make a function for another
>> programmer to use, there are many reasons to keep those
>> errors/warning/informative messages.
>>
>> Messages are one of the way functions communicate with users. =C2 Here's
>> one example:
>>
>>
>> http://mathematica.stackexchange.com/questions/6055/how-to-get-rid-of-warnings-when-using-solve-on-an-equation-with-inexact-coeffici/12
>>
>> The input Solve[-26.81 == 194 k + k*l*32.9&& =C2 22.2 == -74 k+ k*l*
>>
>> 59.7, {k, l}] issued a warning message, prompting the user to check
>> the answer.
>>
>> Another example is FindMinimum[x^2/2 + Cos[x], {x, 1}] (from the
>> docs), where an answer *is* returned, but there's also a warning that
>> it might be incorrect. =C2 Version 5's General::spell messages are yet
>> another example.
>>
>> There's no "writing" and "debugging" step here. =C2 This is the usual way
>> to use the system. =C2 Solve and FindMinimum are high level functions
>> which are probably more commonly typed than used as parts of other
>> functions. =C2 These examples could occur in any usual interactive
>> session of Mathematica.
>>
>> So, to sum up:
>>
>> Usually there's no "development phase" when you work with Mathematica.
>> =C2 If there is, you're probably developing a "library" for users who are
>> going to use it to "program" (actually just use the system
>> interactively), and therefore they'll need messages again.
>>
>> I hope this clears it up.
>>
>> On 29 May 2012 18:07, Christoph Lhotka<christoph.lhotka at fundp.ac.be>
>> =C2 wrote:
>>>
>>> Hi,
>>>
>>> =C2 in my opinion messages in Mathematica are generated during the
>>> evaluation
>>> process to give
>>> some kind of "meta"-information about 1) what is going wrong or 2) what
>>> you
>>> need to know
>>> to check by yourself to know of the returned result is correct.
>>>
>>> I would like to compare this information with the concepts of "errors"
>>> and
>>> "warnings" produced
>>> by a compiler during the process to produce a program.
>>>
>>> Seeing "Mathematica messages" in this flavour any input which produces a
>>> message should be
>>> seen as wrong or not working properly and therefore be modified as long
>>> as
>>> there are no
>>> messages left at all.
>>>
>>> I therefore do not see a reason yet why I should use messages outside the
>>> development
>>> phase of a project.
>>>
>>> Can you provide me with one?
>>>
>>> Thanks,
>>>
>>> Christoph
>>>
>>>
>>>
>>>
>>>
>>> On 05/29/2012 11:47 AM, Szabolcs Horv=C3=A1t wrote:
>>>>
>>>> There were two replies suggesting to use Check[] to abort evaluation
>>>> when a message is generated.
>>>>
>>>> Note that while Check does return a different result if a message was
>>>> generated, it does not actually interrupt evaluation (it completed the
>>>> evaluation of 'expr').
>>>>
>>>> See here for an example:
>>>>
>>>>
>>>>
>>>> http://mathematica.stackexchange.com/questions/5534/check-does-not-interrupt-evaluation-of-the-expression-when-a-message-is-emitted
>>>>
>>>> Please see here for a method that will reliably abort immediately when a
>>>> message is generated.
>>>>
>>>>
>>>>
>>>> http://mathematica.stackexchange.com/questions/1512/how-to-abort-on-any-message-generated
>>>>
>>>> On 2012.05.27. 10:40, Sseziwa Mukasa wrote:
>>>>>
>>>>> Check[expr,Return[]]
>>>>>
>>>>> On May 26, 2012, at 5:11 AM, Ralph Dratman<ralph.dratman at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Is there a simple way to get Mathematica to stop evaluating (like
>>>>>> Interrupt) whenever a message is issued?
>>>>>>
>>>>>> I realize the debugger has that feature, but I would prefer not to use
>>>>>> it in this case.
>>>>>>
>>>>>> Thank you.
>>>>>>
>>>>>> Ralph Dratman
>>>>>>
>



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