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Re: replacement x->y except in Exp[x]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg110905] Re: replacement x->y except in Exp[x]
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 11 Jul 2010 06:18:29 -0400 (EDT)

I stand corrected.

On 7/10/2010 6:23 AM, Andrzej Kozlowski wrote:
> Actually I is a Symbol, before evaluation:
>
> In[90]:= Head[Unevaluated[I]]
>
> Out[90]= Symbol
>
> but it is no loner one after evaluation:
>
> In[91]:= Head[I]
>
> Out[91]= Complex
>
> Andrzej Kozlowski
>
>
> On 10 Jul 2010, at 17:01, Murray Eisenberg wrote:
>
>> I is not a "symbol"!
>>
>> Head[I]
>> Complex
>>
>> 3+I /. I->  -I
>> 3 + I
>>
>> Head[2]
>> Integer
>>
>> (2/3) /. 2->5
>> 2/3
>>
>> Please stop beating the dead horse.
>>
>>
>> On 7/8/2010 8:34 PM, AES wrote:
>>
>>> ...Is it ever a good idea to use ReplaceAll to do word-processing-type
>>> "global find and replace" changes like this?
>>>
>>> Lengthy threads on this NG have pointed out the havoc that this can
>>> wreak if the symbol I is among those replaced, particularly if one
>>> attempts to do I ->   -I.
>>>
>>> Or is I the _only_ symbol in the entire Mathematica vocabulary that
>>> encounters this difficulty?
>>>
>>> (I really would like to know the answer to this question, even if this
>>> is entirely out of curiosity, not any real need.  I've asked it
>>> previously, and never gotten an answer.)
>>
>>
>> --
>> Murray Eisenberg                     murray at math.umass.edu
>> Mathematics&  Statistics Dept.
>> Lederle Graduate Research Tower      phone 413 549-1020 (H)
>> University of Massachusetts                413 545-2859 (W)
>> 710 North Pleasant Street            fax   413 545-1801
>> Amherst, MA 01003-9305
>>
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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