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RE: Constant term in polynomial?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg3342] RE: [mg3326] Constant term in polynomial?
*From*: "Chandler, Seth" <SChandler at UH.EDU>
*Date*: Thu, 29 Feb 1996 03:23:16 -0500
*Sender*: owner-wri-mathgroup at wolfram.com
How about Select[7+ 3 x y - y ^2,AtomQ]
Since the other terms in a polynomial will likely have a Times or Power
head, this might work fairly well.
Seth J. Chandler
Associate Professor of Law
University of Houston Law Center
----------
> From: mathgroup-adm
To: mathgroup at smc.vnet.net
> To: mathgroup
> Subject: [mg3326] Constant term in polynomial?
> Date: Monday, February 26, 1996 2:57AM
>
> Arrgh, I feel stupid asking this question, but I can't think how to do
it:
> how do I find the constant term in a polynomial in several variables in
> Mathematica? For example, the "7" in 7 + 3 x y + y^2 ?
>
> I suppose one way would be to use
>
> Coefficient[Coefficient[7 + 3 x y + y^2,x,0],y,0].
>
> But that's incredibly clunky, especially since I may have fifty or more
> variables in my real-life problem.
>
> I could evaluate the expression under the rule {x->0, y->0}, with the
same
> problem: for fifty variables that's awkward. I could build the rule
using
> Variables[expr], but that's clumsy and seems inefficient.
>
> First[7 + 3 x y + y^2] will work for this one, since the 7 is present and
> appears first in the FullForm representation. But it won't work in
> First[3 x y + y^2], which returns 3 x y.
>
> OK, so I can build a command which computes Variables[First[expr]], and
> if that's empty, returns 0; otherwise returns First[expr]. Also clunky
> IMHO, but it seems the most workable--unless there's some trap I'm
missing?
>
> Or I can introduce an auxiliary variable "one", refer to the polynomial
as
> "7 one + 3 x y + y^2", and ask for Coefficient[expr, one]. Gag! If I
ever
> want to EVALUATE it, I have to remember to use the rule one->1.
>
> There MUST be a standard way to do this, but I can't think of what it
could
> be!
>
> --Ron Bruck
>
>
>
>
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