Re: Dot or Inner ... but not quite

*To*: mathgroup at smc.vnet.net*Subject*: [mg79648] Re: Dot or Inner ... but not quite*From*: Bill Rowe <readnewsciv at sbcglobal.net>*Date*: Wed, 1 Aug 2007 04:58:01 -0400 (EDT)

On 7/31/07 at 6:13 AM, dot at dot.dot (Diamond, Mark) 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? Certainly, there are other ways. But better is fairly subjective. Here are two ways to accomplish the same thing In[7]:= Plus @@@ Thread[l1 l2] Out[7]= {20,49} In[8]:= Plus @@ MapThread[Times, {l1, l2}] Out[8]= {20,49} Note, both of these output what you said you wanted to produce, i.e., In[9]:= 1*{1, 7} + 4*{1, 9} + 3*{5, 2} Out[9]= {20,49} Which is not what your code does, i.e., In[10]:= (#[[1]]*#[[2]]) & /@ Transpose[{l1, l2}] Out[10]= {{1, 7}, {4, 36}, {15, 6}} -- To reply via email subtract one hundred and four