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Re: Just another Mathematica "Gotcha"

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  • Subject: [mg120833] Re: Just another Mathematica "Gotcha"
  • From: David Bailey <dave at>
  • Date: Fri, 12 Aug 2011 05:05:02 -0400 (EDT)
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  • References: <j2069b$6vn$>

On 11/08/2011 10:10, Glenn Carlson wrote:
> Yes, I think it's a matter of precedence.  For example,
> In[1]:= Normal /. b2 ->  0
> Series[a + (b1 + b2) x, {x, 0, 1}] // %
> Out[1]= Normal
> Out[2]= a + (b1 + b2) x
> At my level of proficiency with Mathematica, I shy away from stringing together too many operations. I prefer smaller, more manageable portions.
> It took my brain some time before it allowed me to see [1] as a legitimate operation.  Is [1] just a curiosity? Or is there a situation that would call for such usage?
> Thanks and regards,
> Glenn
I would not describe this as a total curiosity.

1)    There are plenty of situations in which you might want to apply a 
substitution whether or not it will actually 'fire'. You certainly would 
not to have to write code to test if an expression contained b2 before 
applying a replacement operation to remove b2!

2)    Creating a head of an expression that is, itself subject to 
evaluation isn't that unusual. A simple use is to create a synonym of a 

In[673]:= sine=Sin

Out[673]= Sin

In[674]:= sine[0.2]

Out[674]= 0.198669

David Bailey

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