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MathGroup Archive 2006

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TraditionalForm bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66068] TraditionalForm bug?
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 28 Apr 2006 06:33:14 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

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


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