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MathGroup Archive 2004

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Re: Building a list

  • To: mathgroup at
  • Subject: [mg47139] Re: [mg47114] Building a list
  • From: Sseziwa Mukasa <mukasa at>
  • Date: Sat, 27 Mar 2004 01:34:43 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at

On Mar 26, 2004, at 3:56 AM, Mark Coleman wrote:

> Greetings,
> I've got a relatively simple function f[a_,b_,c_,d_], where a and b are
> integers and c and d are lists (of reals), and f returns a real.
> I need to evaluate f on (potentially long) sets of lists and calculate
> a square "matrix" from the possible permutations of the elements in the
> lists. For instance
> If
> xlist={x1,x2,x3}
> I need to calculate
> {{f[a,b,x1,x1],f[a,b,x1,x2],f[a,b,x1,x3]},{f[a,b,x2,x1],f[a,b,x2,x2],f[ 
> a
> ,b,x2,x3]},{f[a,b,x3,x1],f[a,b,x3,x2],f[a,b,x3,x3]}}
> Note that f[a,b,c,d] does not equal f[a,b,d,c].
> My first reaction was that Outer[] might do this, but I cannot seem to
> get it to work. I'd appreciate any suggestions.

Your first reaction was fine:

Outer[f[a, b, ##] &, xlist, xlist]

works.  You could also explicitly use Array, for example

Array[f[a, b, xlist[[#]], xlist[[#2]]] &, {Length[xlist],  

also works.



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