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Re: Variant of inner Product ...


On May 4, 2005, at 12:32 AM, Detlef Müller at smc.vnet.net wrote:

> Hello,
>
> I have the following to do:
>
> Given
>
> In[1]:= A={1,2,3}; B={{a,b},{c,d},{r,s}};
>
> And a Function f, I like to have
>
> Out[2] = {f[1,a],f[1,b]}+{f[2,c],f[2,d]}+{f[3,r],f[3,s]}
>
> The trial
>
> In[8]:=A={1,2,3}; B={{a,b},{c,d,e},{r,s}};
> In[9]:= Inner[f,A,B]
> Out[9]= f[1,{a,b}]+f[2,{c,d,e}]+f[3,{r,s}]
>
> looks promising,
> but if the Lists in B have the same length, "Inner"
> makes something different:
>
> In[15]:=
> A={1,2,3}; B={{a,b},{c,d},{r,s}}; Inner[f,A,B]
>
> Out[16]= {f[1,a]+f[2,c]+f[3,r],f[1,b]+f[2,d]+f[3,s]}
>
> So for now I have an ugly Table-Construction doing the job,
> but I can't imagine there is no elegant and clear solution
> for this ... any suggestions?
>
> Greetings,
>    Detlef

I would try with:

In[42]:=
nn = Tr[Outer[f, A, B, 1]]
Out[42]=
f[1, {a, b}] + f[2, {c, d}] +
   f[3, {r, s}]

and go from there.

János


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