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MathGroup Archive 2004

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Re: Building a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47141] Re: [mg47114] Building a list
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Sat, 27 Mar 2004 01:34:46 -0500 (EST)
  • References: <200403260856.DAA22958@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Mark,

Perhaps this will help:

In[1]:=
xlist = {x1, x2, x3}; 

In[2]:=
mat = Outer[List, xlist, xlist]
Out[2]=
{{{x1,x1},{x1,x2},{x1,x3}},{{x2,x1},{x2,x2},{x2,x3}},{{x3,x1},{x3,x2},{x3,
      x3}}}

In[3]:=
((f[a, b, Sequence @@ #] & ) /@ # & ) /@ mat
Out[3]=
{{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]}}

Tomas Garza
Mexico City

----- Original Message ----- 
From: "Mark Coleman" <mark at markscoleman.com>
To: mathgroup at smc.vnet.net
Subject: [mg47141] [mg47114] Building a list


> 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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