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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