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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106076] Re: [mg106051] Re: [mg106017] More /.{I->-1} craziness
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Fri, 1 Jan 2010 05:32:14 -0500 (EST)
  • References: <200912300915.EAA17299@smc.vnet.net>
  • Reply-to: drmajorbob at yahoo.com

> But anything concerning
> infinite quantities is bound to be so special that nothing about
> handling of Infinity would really surprise me.

In short, if I may presume to paraphrase... you don't expect any rules to  
apply. You'll determine the behavior of infinite quantities in each  
setting you meet, independently.

I do the same thing myself, every time I write a Mathematica statement. I  
neither trust the documentation, nor MY MEMORY of the documentation or  
previous experience. It's common for me to push F1 on functions I've used  
hundreds of times and try it again to see how it works, in case it changed  
or I've missed something. If it doesn't do what documentation says or what  
I remember, I count it as merely typical, and I try something else.

That approach is reliable, but sometimes tiring (in any language).

Bobby

On Thu, 31 Dec 2009 02:16:47 -0600, Murray Eisenberg  
<murray at math.umass.edu> wrote:

> These "seemingly wildly inconsistent" results are explained, in large
> part, by what has been posted in this thread earlier, and in particular
> by [mg106003] from Daniel Lichtblau.  Perhaps "at first surprising"
> would be a much better description tan "seemingly wildly inconsistent".
>
> Try these:
>
>    FullForm /@ {-I, -E, -Pi, -Infinity}
>    AtomQ /@ {-I, -E, -Pi, -Infinity}
>
> To my mind, the only possible surprise here -- simply because I never
> looked at it before, concerns -Infinity.  But anything concerning
> infinite quantities is bound to be so special that nothing about
> handling of Infinity would really surprise me.
>
> AES 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.)
>>
>


-- 
DrMajorBob at yahoo.com


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