Re: How to isolate the constant in a two variable
- To: mathgroup at smc.vnet.net
- Subject: [mg113482] Re: How to isolate the constant in a two variable
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Sat, 30 Oct 2010 04:39:06 -0400 (EDT)
expr = 4 X*X + 3 Y*Y + 2 X*Y + 1;
If there is always a constant
expr[[1]]
1
But note that if there is no constant then
(expr - 1)[[1]]
4 X^2
Fix with
Module[{c = expr[[1]]},
If[NumericQ[c], c, 0]]
1
The following are more robust
Select[expr, NumericQ]
1
Using Coefficient
Fold[Coefficient[#1, #2, 0] &,
expr, Variables[expr]]
1
Using coefficientList
Module[{vars = Variables[expr]},
CoefficientList[expr,
vars][[Sequence @@ Table[1, {Length[vars]}]]]]
1
Bob Hanlon
---- "Eduardo M. A. M.Mendes" <emammendes at gmail.com> wrote:
=============
Hello
I know that Coefficient can isolate the coefficient relate to the variables
in an equation but I wonder how the constant could be retrieved.
Something like
4X*X+3Y*Y+2X*Y+1
How to get to isolate the constant 1?
Many thanks
Ed