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Expression manipulation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88722] Expression manipulation
  • From: David <David.B.A.Epstein at googlemail.com>
  • Date: Wed, 14 May 2008 06:04:50 -0400 (EDT)

When trying to simplify an expression by hand, one carries out various
kinds of steps:
1. Replace a subexpression that occurs repeatedly by a single symbol.
2. Multiply numerator and denominator of some subexpression by the
same factor.
3. Cancel particular factors in numerator and denominator of some
subexpression.
4. Gather together two subexpressions that were added together, and
rewrite with a common denominator.
5. Remove common factors.

etc. etc. etc.

Using Part, one can of course access any particular subexpression. But
this is time-consuming and clumsy. I find that I need trial and error
to access the correct subexpression. Once I've accessed it, I often
have difficulty in persuading Mathematica to perform the desired
operation. And then I have trouble putting the subexpression back into
place. It's something like 20 times slower than working with pencil
and paper. HOWEVER pencil and paper calculations are more prone to
stupid arithmetic errors, particularly if the computation is a long
one.

I have been unable to find a convenient way of doing this in
Mathematica. I use version 5.2, but because of my University's site
license, I have access to more recent versions. Would it help to
change?

Can anyone point me to a tutorial where experts use Mathematica to do
a typical pencil and paper computation?

Thanks a lot. Please copy replies to my personal email address as I
don't look at the newsgroup very often.

David


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