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 > > > > ==== [MESSAGE SEPARATOR] ====