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Re: Show left hand side

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  • Subject: [mg111144] Re: Show left hand side
  • From: Helen Read <hpr at>
  • Date: Thu, 22 Jul 2010 05:40:18 -0400 (EDT)
  • References: <i20q3s$kdf$> <i26kr1$9d1$>
  • Reply-to: HPR <read at>

On 7/21/2010 7:14 AM, Helen Read wrote:
> On 7/19/2010 2:07 AM, David Park wrote:
>> When everything is in one cell you can safely use % and %% without worrying
>> about order of evaluation.
> As for % and %%, I never use them, and I certainly don't teach them.
> Using % in a single cell vs. multiple cells is a distinction that my
> students are likely not to make, with dire consequences. When I first
> started teaching with Mathematica ~15 years ago (!), the use of % was
> one of the two biggest sources of problems for my students. A couple of
> years in, life got much better when I made a conscious decision not to
> introduce the % notation to my students, and to discourage its use by
> the few students who discover it (or even worse, the dreaded Out[17]
> notation, which is a living nightmare) on their own.
> When I stopped teaching %, I realized I didn't need it either, and I
> stopped using it myself. Nobody misses %, least of all me.

One more comment about the % and %%. I remember that they were useful 
way back in the olden days, when I was using Mathematica on unix 
workstations. There was no notebook interface -- it was line in, line 
out, and there was no way to edit something you had already entered and 
evaluated. About the only way to refer back to something you had already 
done was with % and %% etc., or the Out[23] notation. This was OK at the 
time, because it was all done sequentially, input/output, with no going 
back. But with the notebook interface, we find ourselves jumping around 
the notebook, editing and re-evaluating, saving the whole thing and 
coming back another time when the % and Out[] numbers will be completely 
changed. With all of that going on in a notebook, the use of % and %% 
and %7 and Out[113] etc. is far more trouble than it's worth, as far as 
I'm concerned. If the notebook interface had been around at the very 
beginning, I'm not sure Wolfram would have ever included the % and %% 

Helen Read
University of Vermont

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