Re: Expression manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg88718] Re: Expression manipulation*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Wed, 14 May 2008 06:59:52 -0400 (EDT)*Organization*: University of Bergen*References*: <g0edhe$9eq$1@smc.vnet.net>

David wrote: > 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? > I prefer pen and paper to Mathematica when manipulating simple expressions. Mathematica is useful when working with large expressions, e.g. high-order polynomials or rational functions, etc. Don't use Part during interactive work. Instead take a look at ReplaceAll, Together, Expand, ExpandAll, Cancel, etc. Or just copy and paste when you need to extract a particular subexpression. http://reference.wolfram.com/mathematica/guide/FormulaManipulation.html > Thanks a lot. Please copy replies to my personal email address as I > don't look at the newsgroup very often. This just tells us that you don't really care about the reply ... so fewer people will bother to answer ...