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MathGroup Archive 2007

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& without #

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73042] & without #
  • From: "Kristen W Carlson" <carlsonkw at gmail.com>
  • Date: Tue, 30 Jan 2007 23:40:34 -0500 (EST)

Hi,

From Built-in Functions/Cases, here is this (undocumented?) usage of &
without #:

L=Array[Random[Integer,10]&,20]

{4,5,9,6,8,5,4,0,9,4,5,2,10,6,3,7,4,2,2,8}

Here is what happens without the &:

L=Array[Random[Integer,10],20]

{3[1],3[2],3[3],3[4],3[5],3[6],3[7],3[8],3[9],3[10],3[11],3[12],3[13],3[
 14],3[15],3[16],3[17],3[18],3[19],3[20]}

Can someone who understands this please explain as completely as you
can, including how & and # work
together, given the behavior of & alone. And is this documented anywhere?

This might help and I also post it to help illuminate for those who
haven't seen this & usage; it is from Andrzej a while ago (Andrzej I
hope you don't mind):

In general it means a constant function. For example 3& will return 3
with any argument. But the are at least two "special" functions,
which will work like "variable constants" when used in this way. One
of them is Random[]& (and various variants of it). Another is Unique
[symbol]&, which on every evaluation will produce a unique name based
on "symbol".

Kris



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