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MathGroup Archive 2007

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Re: comparing rewite rules

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78341] Re: comparing rewite rules
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 28 Jun 2007 06:29:25 -0400 (EDT)
  • References: <f5vsg8$l2f$1@smc.vnet.net>


Hi Roger,

you are trying to compare ordered list. Therefore, the order is 

important. To circumvent this, define a new head e.g. myList and give it 

the Orderless attribute:

SetAttributes[myList, Orderless]

myList[yy -> 4, y -> 3] == myList[y -> 3, yy -> 4]

this now reults in True.

hope this helps, Daniel





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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