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MathGroup Archive 2007

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Re: Dot or Inner ... but not quite

  • To: mathgroup at smc.vnet.net
  • Subject: [mg79673] Re: Dot or Inner ... but not quite
  • From: Adriano Pascoletti <adriano.pascoletti at gmail.com>
  • Date: Wed, 1 Aug 2007 05:11:19 -0400 (EDT)
  • References: <f8n2rc$lp9$1@smc.vnet.net>

On Jul 31, 12:27 pm, "Diamond, Mark" <d... at dot.dot> wrote:
> I have two equi-length lists, the first of number, the second of
> (equi-length) lists of numbers , such as
>
> l1={1,4,3};
> l2={{1,7},{1,9},{5,2}};
>
> I want to produce 1*{1,7}+4*{1,9}+3*{5,2}
>
> It looks so close to Inner that I thought I could use it in some form, but I
> have ended up using
>
> (#[[1]]*#[[2]])& /@ Transpose[{l1,l2}]
>
> Is there a better way using one of the builtin functions with which I am
> unfamiliar?
>
> Cheers,
>
> Mark Diamond

Inner[f, l1, l2] gives {f[1, 1] + f[3, 5] + f[4, 1], f[1, 7] + f[3, 2]
+ f[4, 9]}
so
Inner[Times, l1, l2] gives the answer to your question: {20,49}

Adriano Pascoletti



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