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MathGroup Archive 2006

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Re: TraditionalForm bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66069] Re: TraditionalForm bug?
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 28 Apr 2006 06:33:17 -0400 (EDT)
  • References: <7B896DFE-0B74-4E2B-A5C0-D6FCBDE2B69F@mimuw.edu.pl>
  • Sender: owner-wri-mathgroup at wolfram.com

On 27 Apr 2006, at 22:06, Andrzej Kozlowski wrote:

> I just noticed something in my version of Mathematica:
>
> $Version
>
> 5.1 for Mac OS X (October 25, 2004)
>
> which certainly looks like a bug that should have been spotted a  
> long time ago. The "bug" is simply this. Evaluate
>
> In[14]:=
> Sin'
>
> Out[14]=
> cos(#1)&
>
> This is fine. But now simple convert the above input to  
> TraditionalForm and evaluate it again:
>
> In[15]:=
> \!\(\*FormBox[
>   SuperscriptBox["sin", "â?²",
>     MultilineFunction->None], TraditionalForm]\)
>
> Out[15]=
> \!\(\*FormBox[
>   SuperscriptBox["sin", "â?²",
>     MultilineFunction->None], TraditionalForm]\)
>
> What happens is that Mathematica converts Sin` to sin` and then  
> forgets what sin means. This does not happen if you do the same  
> with an argument:
>
> In[17]:=
> Sin'[x]
>
> Out[17]=
> cos(x)
>
> In[18]:=
> \!\(\*FormBox[
>   RowBox[{
>     SuperscriptBox["sin", "â?²",
>       MultilineFunction->None], "(", "x", ")"}], TraditionalForm]\)
>
> Out[18]=
> cos(x)
>
> The embarrassing thing is that I discovered this while trying to  
> show my students the advantages of functional notation, and in  
> particular the fact that one can refer to functions and their  
> derivatives without introducing unnecessary variables. Of course  
> this is true, but if you sue TraditionalForm form input! This  
> reminds me that there was recently a discussion of whether  
> TraditionalForm is or is not suitable for this purpose.  I recall  
> that Paul Abbott and Daniel Lichtblau expressed opposing views and  
> I was tempted to enter the fray but decided to stay out, because  
> while my heart sided with Paul my brain did not. As is often the  
> case the brain seems to have been right.
>
> Andrzej Kozlowski


Perhaps I was a bit too harsh, since this works:

(sin(#)&)'


cos(#1)&

So things are not quite as bad as I wrote above, we can still use  
functional notation and derivatives as long as we remember to write  
sin(#)& instead of sin etc.
Still, this means that TraditionalForm is not quite as "traditional"  
as one would wish it to be.

Andrzej Kozlowski


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