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Re: Re: coefficient of a polynomial term

• To: mathgroup at smc.vnet.net
• Subject: [mg59406] Re: [mg59397] Re: coefficient of a polynomial term
• From: Andrzej Kozlowski <akozlowski at gmail.com>
• Date: Mon, 8 Aug 2005 06:17:09 -0400 (EDT)
• References: <dd4em8$hm6$1@smc.vnet.net> <200508080734.DAA03484@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

On 8 Aug 2005, at 09:34, Bhuvanesh wrote:

>> There are also undocumented algebra functions whose
>> output contains the coefficients of a polynomial,
>> for example
>>
>> s=Internal`DistributedTermsList[poly,{x,y}]
>>
>> {{{{3, 0}, 1}, {{2, 0}, 2}, {{1, 1}, 3}, {{0, 2}, 4}},
>> {x, y}}
>>
>> You can extract the coefficients with, for example:
>>
>> s[[1,All,1]][[All,1]]
>>
>> {3,2,1,0}
>>
>
> You meant:
>
> In[1]:= poly = 2 x^2 +3 x*y +4 y^2+x^3;
>
> In[2]:= s = Internal`DistributedTermsList[poly,{x,y}]
>
> Out[2]= {{{{3, 0}, 1}, {{2, 0}, 2}, {{1, 1}, 3}, {{0, 2}, 4}}, {x, y}}
>
> In[3]:= s[[1,All,2]]
>
> Out[3]= {1, 2, 3, 4}
>
> The result of DistributedTermsList looks like:
>
> {{{expvec1,coef1}, {expvec2,coef2}, ...}, variables}
>
> where "expvec" stands for "exponent vector". There's also the  
> inverse, which converts the result of DistributedTermsList back to  
> the explicit polynomial form:
>
> In[4]:= Internal`FromDistributedTermsList[s]
>
>            2    3              2
> Out[4]= 2 x  + x  + 3 x y + 4 y
>
> Bhuvanesh,
> Wolfram Research.
>
>


Thanks. I must have have been affected by insanity (temporary, I  
hope) when I wrote that last line...

Andrzej

• References:
  • Re: coefficient of a polynomial term
    • From: Bhuvanesh <lalu_bhatt@yahoo.com>