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MathGroup Archive 2007

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Re: comparing rewite rules

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78364] Re: [mg78329] comparing rewite rules
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 29 Jun 2007 05:45:09 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

r1 = {yy -> 4, y -> 3};

r2 = {y -> 3, yy -> 4};

Sort[r1] == Sort[r2]

True

var = Union[(First /@ r1), (First /@ r2)];

(var /. r1) == (var /. r2)

True


Bob Hanlon

---- dbsearch04 at yahoo.com wrote: 
> Hello Mathematica UG:
> 
> I input these 2 simple rewrite rule sets into Mathematica V5:
> 
> - {yy -> 4, y -> 3}
> 
> - {y -> 3, yy -> 4}
> 
> I just want to compare these 2 simple rules for equality. I tried:
> 
> - define each one and use % == %% (this just gives: {yy -> 4, y -> 3}
>  == {y -> 3, yy -> 4} )
> - making a symbol for each rule set and using ==, such as rul0 ==
> rul1,
>  it just echoes my input
> 
> I also tried to replace the rules in an expression. If the replaced
> result evaluates to a simple expression, it is OK but, it still fails
> sometime when Mathematica reorders expressions, such as when x-1 becomes -1 +
> x
> 
> Is it possible to determine in my code that 2 "rule lists" are the
> same?
> 
> Of course, in the general case, I will have many more rules than just
> these 2 small lists (e.g. Solve[] output).
> 
> Thanks in advance.
> 
> Regards..Roger
> 
> 



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