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Re: More /.{I->-1} craziness

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106042] Re: More /.{I->-1} craziness
  • From: Valeri Astanoff <astanoff at gmail.com>
  • Date: Thu, 31 Dec 2009 03:14:58 -0500 (EST)
  • References: <hhf5s3$h4o$1@smc.vnet.net>

On 30 d=E9c, 10:17, AES <sieg... at stanford.edu> wrote:
> The more I play with these I->-I substitution rules, the more seemingly
> wildly inconsistent results emerge.  For example:  
>
>    In[1]:= -I/.I->-I
>
>    Out[1]= -I
>
>    In[3]:= -E/.E->-E
>
>    Out[3]= << The Esc e e Esc symbol >>
>
>    In[4]:= -Pi/.Pi->-Pi
>
>    Out[4]= \[Pi]
>
>    In[5]:= -Infinity/.Infinity->-Infinity
>
>    Out[5]= -\[Infinity]
>
> (In/Out[2] is removed because it was an irrelevant cell.)

Good day,

Caveat substitutor !

That's not full craziness : what we see is *not*
what we get because pattern recognition is not
based on mathematical equivalence but on
structure equivalence (given by FullForm).

Imho, when applying a rule  lhs -> rhs
it's a risky practice to use the same symbol
in 'lhs' and 'rhs', because, very often, there is
no easy way to check what has been done.

Anyway, for occasional users, you're right : it's crazy!

--
Valeri Astanoff


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