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MathGroup Archive 2006

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Re: Array

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69239] Re: [mg69220] Array
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sun, 3 Sep 2006 23:46:23 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 3 Sep 2006, at 06:39, Bruce Colletti wrote:

> The command:
>
>    {A[1], A[2], A[3]} = {1, 2, 3}
>
> assigns a value to each A-variable.  However, the command:
>
>    Array[A,3] = {1,2,3}
>
> generates an error message.
>
> What is the difference between the two lines?
>
> Thankx.

>
> Bruce
>

Set (=) works in a special way when you make assignments to lists, as  
stated in the Help:

?Set
"lhs = rhs evaluates rhs and assigns the result to be the value \
of lhs. From then on, lhs is replaced by rhs whenever it appears.  
{l1, l2, \
... } = {r1, r2, ... } evaluates the ri, and assigns the results to  
be the \
values of the corresponding li.

This is why your first example works. However, since  Set does not  
evaluate its first argument, it tries to assign a rule to the symbol  
Array, which it can't do since Array is Protected. Hence what you  
should use is:

Evaluate[Array[A,3]]={1,2,3}

which will work exactly as the first example.

Andrzej Kozlowski




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