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Re: Question re I->-I

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  • Subject: [mg106550] Re: [mg106508] Question re I->-I
  • From: "David Park" <djmpark at>
  • Date: Sat, 16 Jan 2010 06:10:27 -0500 (EST)
  • References: <19411026.1263546688785.JavaMail.root@n11>

Taking a negative (which operates on the whole number) is NOT the same as
taking a conjugate (which modifies only one part.)

In this respect Rational numbers behave the same as Complex numbers. Do you
expect a rule that only works on the denominator of a Rational to work for
all expressions?

3/2 /. (1/2 -> 1/4)  
% // FullForm  

Rational[3, 2] 

But this works:

3/2 /. Rational[a_, b_] -> Rational[a, 2 b] 


Mathematica must have a module that handles the processing of ALL NUMBERS
and it's a little futile to pull on one thread and ignore how this might
affect everything else.

The present system is not inconsistent, or illogical, or difficult to learn.
Just learn it.

David Park
djmpark at  

From: AES [mailto:siegman at] 

Alternative question:

*  Type in a rational polynomial in a simple variable "s" (format it any 
way you like), and apply this sRule.  Is there any way you can reformat 
this rational polynomial, without changing its meaning, so as to get 
different results when the sRule is applied?

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