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MathGroup Archive 2004

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Re: Re: canonical mathematical expression represenation?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52534] Re: [mg52511] Re: [mg52484] canonical mathematical expression represenation?
  • From: "Blimbaum, Jerry AA R22" <jerry.blimbaum at navy.mil>
  • Date: Wed, 1 Dec 2004 05:57:55 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

David....

Mathgroup to me is like Golf....both have really humbled me....

Jerry blimbaum

-----Original Message-----
From: David Park [mailto:djmp at earthlink.net] 
To: mathgroup at smc.vnet.net
Subject: [mg52534] [mg52511] Re: [mg52484] canonical mathematical expression
represenation? 



Yes it is annoying the way Mathematica tends to get the minus signs
where we would prefer not to have them. One way to fix this, in simple
expressions at least, is to Map Minus to the two factors you would wish
to change.

Sum[a^k, {k, 0, M}]
MapAt[Minus, %, {{1, 1}, {2}}]
(-1 + a^(1 + M))/(-1 + a)
(1 - a^(1 + M))/(1 - a)

I find that it is almost always possible to manipulate expressions to
the form you want, textbook form say, but it is a bit of an art and
sometimes even I have to come to MathGroup to learn the trick.


David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

From: nospam nospam [mailto:nospam_please at nospam.com]
To: mathgroup at smc.vnet.net

I noticed that Mathematica represents expressions with
some specific 'way' or order.

For example,

Sum[a^k, {k, 0, M}]

gives
          -1 + a^(1+M)
         -------------
            -1 + a


How can I make it display the expression, in what I would consider a
more 'natural' way, as follows

           1 - a^(1+M)
         -------------
            1 - a

I am sure there is a way to do, and why do you think Mathematica does it
the way it does? what is the logic of how it represents things? is there
a command to convert the first output to the second? I tried few
commands, but can not figure it out.

thank you,
--nospam




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