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Re: Debracketing array symbols

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92237] Re: Debracketing array symbols
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 23 Sep 2008 07:36:46 -0400 (EDT)

On 9/22/08 at 5:25 AM, carlos at Colorado.EDU wrote:

>A related question   A={A[1], A[2], A[3], A[4]}  produces infinite
>recursion in 4.2 and 5.2 (NB - I prepare all coursework with 4.2 for
>compatibility with some remote students in industry)
>Is the symbol A used on the RHS?

Yes.

>{A[1], A[2], A[3], A[4]} //FullForm   just shows
>List[A[1],A[2],A[3],A[4]]  which does not tell me much. Where is the
>role of A in the RHS explained in the documentation?.

Per basic Mathematica syntax, square brackets are *always* used
to delimit arguments to functions. So, the syntax A[1] is
interpreted as the function named A to be evaluated at the
argument 1.

Given this the rhs of what you wrote defines a list where the
function A is evaluated at 4 different values. Of course since A
has not yet been defined the evaluator can only return the
unevaluated form of A at the four arguments.

But now the rest of what you wrote attempts to define A as the
list of four instances of A evaluated at 4 points. This
obviously is an infinite recursion as indicated by the error message.


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