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Re: beginner question about syntax

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109086] Re: beginner question about syntax
  • From: dr DanW <dmaxwarren at gmail.com>
  • Date: Mon, 12 Apr 2010 22:59:19 -0400 (EDT)
  • References: <hputp3$lh7$1@smc.vnet.net>

AK,
Whenever Mathematica seems to be doing something nonsensical (based on
what you are seeing on the screen,) then FullForm[] is your friend.
What you see in your notebook are expressions formatted to be human-
readable.  FullForm[] lets you see the structure that Mathematica is
actually working with.

In[14]:=
FullForm[a]

Out[14]//FullForm= a

In[15]:=
FullForm[a + b + c]

Out[15]//FullForm= Plus[a, b, c]

Mathematica expressions are always in the form of head[elem1,
elem2, ...].  Of course, you may not see that structure explicitly
unless you use FullForm[].  The function Map[f, expr] applies f to
each element on the first level in expr.  Looking at the FullForm of
a, you see that a has no first level (it is all head), thus there is
nothing to Map f to.   Plus[a,b,c] has the head Plus and three
elements (a, b, and c) at the first level, so f gets mapped to them.

Hope this helps,
Daniel


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