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Re: Simplify

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91096] Re: Simplify
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Wed, 6 Aug 2008 05:04:25 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <g791is$9ng$1@smc.vnet.net>

Cetin Haftaoglu wrote:

> I have a simple question about to simplify a expression (a list/matrices). I
> have a list like
> 
> {2 cet1, 0, -2 cet1, cet1, 0, -cet1}
> 
> And I want to extract if possible the factor cet1, so I become a list like
> 
> cet1{2, 0, -2, 1, 0, -1}

Note that the above expression is *not* a list: This is the product of a 
symbol by a list. Evaluating such an expression will result in the 
original list (cet1 is distributed over the list).

> How can I extract the factor?

Among many other methods, you could use a transformation rule or a 
function such as *Coefficient[]* (Note that the last expression uses the 
non-commutative multiplication sign "**" to prevent distributivity):

   In[1]:=
     lst = {2 cet1, 0, -2 cet1, cet1, 0, -cet1}
     lst /. cet1 -> 1
     Coefficient[lst, cet1]
     cet1 (lst /. cet1 -> 1)
     cet1 ** (lst /. cet1 -> 1)

   Out[1]= {2 cet1, 0, -2 cet1, cet1, 0, -cet1}

   Out[2]= {2, 0, -2, 1, 0, -1}

   Out[3]= {2, 0, -2, 1, 0, -1}

   Out[4]= {2 cet1, 0, -2 cet1, cet1, 0, -cet1}

   Out[5]= cet1 ** {2, 0, -2, 1, 0, -1}


Regards,
-- Jean-Marc


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