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Re: Multiplying Polynomials

  • To: mathgroup at smc.vnet.net
  • Subject: [mg117911] Re: Multiplying Polynomials
  • From: TBone at giganews.com
  • Date: Mon, 4 Apr 2011 06:29:37 -0400 (EDT)
  • References: <in6kh7$2iu$1@smc.vnet.net> <in86kl$9un$1@smc.vnet.net>

On 2011-04-02 17:06:13 -0500, Daniel Lichtblau said:

> ----- Original Message -----
>> From: "TBone" <TBone at yahoo.com>
>> To: mathgroup at smc.vnet.net
>> Sent: Saturday, April 2, 2011 2:41:16 AM
>> Subject:  Multiplying Polynomials
>> This is very simple and I freely confess my ingnorance.
>> 
>> I'm trying to set up a generating function to count some letters of
>> the
>> alphabet. Specifically, I need to multiply two polynomials in the
>> variable x, do some surgery on the result, and continue with another
>> letter.
>> 
>> Here is my problem.
>> 
>> I start with:
>> 
>> expand[(1+ax+a^2x^2+...)*(1+bx+b^2x^2+...)]
>> 
>> and continue with:
>> 
>> expand[(1+ax+bx+abx^2+...)*(1+cx+c^2x^2+...)]
>> 
>> Howerver, it chokes on the following:
>> 
>> expand[(1 + a x + b x + c x + a^2 x^2 + a b x^2 + b^2 x^2 + a c x^2 +
>> b
>> c x^2 +
>> c^2 x^2 + a^2 b x^3 + a b^2 x^3 + a^2 c x^3 + a b c x^3 + b^2 c x^3 +
>> a c^2 x^3 + b c^2 x^3 + a^2 b^2 x^4 + a^2 b c x^4 + a b^2 c x^4 +
>> a^2 c^2 x^4 + a b c^2 x^4 + b^2 c^2 x^4 + a^2 b^2 c x^5 + a^2 b c^2
>> x^5 +
>> a b^2 c^2 x^5 + a^2 b^2 c^2 x^6)*(1 + dx + d^2 x^2)]
>> 
>> What gives?
>> 
>> TIA!!
>> 
>> --TB
> 
> Dunno, from this description. No idea what you expected.
                                                         
^^^^^^^^^^^^^^^^^^^^^^^^^

I guess I expected the Free-Form Input to figure out what was needed.  
It seems to work magically. :)

Using "Expand" and a different grouping of coefficients works.

Thanks for the help everyone!

--TB


> 
> 
> Daniel Lichtblau
> Wolfram Research




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