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MathGroup Archive 2004

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RE: Building a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47137] RE: [mg47114] Building a list
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 27 Mar 2004 01:34:40 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Mark,

xlist = {x1, x2, x3};

Outer[f[a, b, #1, #2] &, xlist, xlist]
{{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]}}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 


From: Mark Coleman [mailto:mark at markscoleman.com]
To: mathgroup at smc.vnet.net

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.

Thanks,

Mark



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