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Re: From list to list of arguments

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113301] Re: From list to list of arguments
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sat, 23 Oct 2010 07:03:37 -0400 (EDT)

On 10/22/10 at 1:36 AM, sam.takoy at yahoo.com (Sam Takoy) wrote:

>Suppose I have a list of arrays, say g = {a, b, c} where a, b, and c
>are arrays, and I would like to calculate

>Outer[Times, a, b, c]

>how do I do it?

Perhaps

Fold[Outer[Times, #1, #2] &, a, {b, c}]

It is unclear to me what result you are looking for.

>I tried

>Apply[Outer[Times,#]&, g], as in Apply[Outer[Times, #] &, {{1},
>{1}}], but that does not yield the right answer. So the question is:
>how does one convert a list {a, b, c} into arguments to a function
>of variable number of arguments?

Use Sequence. For example:

In[1]:= f[x_, y_] := x y

In[4]:= testList = {2, 4};
f[Sequence @@ testList]

Out[5]= 8

of course for this toy example, f@@testList would obviously do
the same thing.

>An auxiliary question: within the function f[x__] := ... what kind
>of object is x? It's not a list, but what is it?

It is a sequence of one or more arbitrary things. Look up
Sequence in the Documentation Center



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