Re: Dot or Inner ... but not quite

• To: mathgroup at smc.vnet.net
• Subject: [mg79653] Re: [mg79622] Dot or Inner ... but not quite
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Wed, 1 Aug 2007 05:00:40 -0400 (EDT)

```l1 = {a1, a2, a3};
l2 = {{b1, b2}, {c1, c2}, {d1, d2}};

Total[(#[[1]]*#[[2]]) & /@ Transpose[{l1, l2}]]

{a1 b1+a2 c1+a3 d1,a1 b2+a2 c2+a3 d2}

Total[l1*l2]

{a1 b1+a2 c1+a3 d1,a1 b2+a2 c2+a3 d2}

% == %%

True

Bob Hanlon

---- "Diamond 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
>
>
>

```

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