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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: [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)
  • Reply-to: hanlonr at cox.net

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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