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MathGroup Archive 1996

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Re: More "Logical" functions?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4230] Re: [mg4144] More "Logical" functions?
  • From: "Edward G. Neuman" <edneuman at math.siu.edu>
  • Date: Tue, 18 Jun 1996 03:28:27 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Scott Herod wrote:

>I often find myself trying to solve big sets of polynomial equations.
>I realize that there are Groebner basis packages for use in this but
>many times I can get by with Reduce and Solve.  My problem is this:
>
>Often I get results like
>
>   {{ x -> 0 },  {x -> 0, y -> 5 },  {x -> 0, z -> -2}, ... }
>
>where {x -> 0} is common to all of the terms.  I would like to be able
>to factor out the x=0 from each equation.  I don't need to see everything
>else if x has to be zero anyway.
>
>Currently I'm doing a LogicalExpand[results && x != 0] to see the cases
>where x does not have to be zero, but something to factor the x -> 0
>would be nicer.
>
>Does anyone know of an existing package do Logical expression operations?
>
>Scott Herod
>(sherod at newton.colorado.edu)
>
>
>

To delete from your list expressions like x->c, where c is a number, you can
use the rewrite-rule capability of Mathematica:

 a={{x->0},{x->0,y->5},{x->1,y->0}};
rule1=#/.{x->c_,y___}->{y}&;
a//rule1
{{}, {y -> 5}, {y -> 0}}

===============================================================================
 Edward Neuman                    Phone: (618) 453-6501
 Department of Mathematics        Fax:   (618) 453-5300
 Southern Illinois University     E-mail: edneuman at math.siu.edu
 Carbondale,  Ill. 62901-4408     
 WWW: http://www.science.siu.edu/mathematics/neuman/ 


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