Re: Re: Simplify and Gather Terms in a Polynomial

• To: mathgroup at smc.vnet.net
• Subject: [mg46471] Re: [mg46448] Re: Simplify and Gather Terms in a Polynomial
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Fri, 20 Feb 2004 00:29:15 -0500 (EST)
• References: <c0uu2k\$e74\$1@smc.vnet.net> <200402190801.DAA14856@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```On 19 Feb 2004, at 09:01, Adam Smith wrote:

> Manipulating an expression from one form to another is always tricky
> in Mathematica.  But here is my suggestion for this case
>
> In[16]:=
> x*Expand[Simplify[y*(x+x^2)/x]]
>
> Out[16]=
> x (y+x y)
>
> This is clearly an odd way to do it and only works for this specific
> case.  Perhaps some of the gurus know a more generally applicable
> approach.
>
> In my opinion Mathematica is not really designed to transform one form
> to another.  If I want to check whether two forms are equivalent, I
> subtract them and use Simplify or FullSimplify to confirm that their
> difference equals 0.  Sometimes it is necessary to apply things like
> Expand, PowerExpand, etc. as intermediate steps.
>
>
>
> sabrinacasagrande at hotmail.com (sabbri) wrote in message
> news:<c0uu2k\$e74\$1 at smc.vnet.net>...
>> I have two equivalent polynomial expressions. In the second, which
>> should derive from the first, terms are gathered respecting to a
>> particular variable. for example:
>>  y(x+ x^2)
>> I want to make it gathered for x
>> x(y+yx)
>> How can I give this command?
>
>
>

It is true that Simplify are difficult to use to achieve the desired
transformation, because of the elusive nature of "simplification". But
as long as you restrict yourself only to polynomials then by using
PolynomialReduce (and sometimes GroebnerBasis) together with such basic
transformations as Expand and Factor, you should be perform essentially