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MathGroup Archive 1995

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Re: Rule Writing for x and 1/x

  • To: mathgroup at christensen.cybernetics.net
  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg838] Re: [mg785] Rule Writing for x and 1/x
  • From: Allan Hayes <hay at haystack.demon.co.uk>
  • Date: Tue, 25 Apr 1995 02:19:24 -0400

D Reece writes

>Is there a way to write a single rule in MMA which will turn J/s  
>into W and s/J into 1/W?

Here is one solution

In[1]:=
	{s/J,J/s}//.{a:(s/J) |(J/s)  :> (a/.J->s W)}
Out[1]=
	 1
	{-, W}
 	 W

But for complicated expressions you might find it better to use  
AlgebraicRules, or my package AlgebraicRulesExtended (on  
MathSource).

In[2]:=
	{Sin[5 + a s^2/J],Sqrt[J]/s/ b, s/J, J/s}/.
		AlgebraicRulesExtended[ J/s == W]
Out[2]=
	         a s   Sqrt[s W]  1
	{Sin[5 + ---], ---------, -, W}
	          W       b s     W

Or, if you prefer J to s

In[3]:=
	{Sin[5 + a s^2/J],Sqrt[J]/s/ b, s/J, J/s}/.
		AlgebraicRulesExtended[ J/s == W,{s,J}]
Out[3]=
	         a J       W      1
	{Sin[5 + ---], ---------, -, W}
	          2    b Sqrt[J]  W
		 W
		
Allan Hayes
hay at haystack.demon.co.uk


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