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Re: sum with lists

• To: mathgroup at smc.vnet.net
• Subject: [mg40555] Re: sum with lists
• From: bobhanlon at aol.com (Bob Hanlon)
• Date: Thu, 10 Apr 2003 03:36:53 -0400 (EDT)
• References: <b70npo$9gd$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

n=20;

d = Table[ks=ToString[k];
      ToExpression["{x"<>ks<>
          ",y"<>ks<>",z"<>ks<>"}"],
      {k,0,n}];

Tr[First[#]*Last[#]& /@ Take[d,n/2+1]]

or


(First /@ #).(Last /@ #)&[Take[d,n/2+1]]


Bob Hanlon

In article <b70npo$9gd$1 at smc.vnet.net>, "Nathan Moore" <nmoore at physics.umn.edu>
wrote:

<< 
Subject:	sum with lists
From:		"Nathan Moore" <nmoore at physics.umn.edu>
To: mathgroup at smc.vnet.net
Date:		Wed, 9 Apr 2003 09:06:00 +0000 (UTC)

Another list question.  Suppose that I have the list 
    d={
    {x0,y0,z0},
    {x1,y1,z1},
    {x2,y2,z1},
    ...
    {xn,yn,zn}}

and now I'd like to calculate the sum, 
    Sum[x[i]*z[i],{i,0,n/2}]

I tried 
    Sum[d[[i, 1]]*d[[i, 3]], {i, 0, 10}]
with little success

thanks,

Nathan Moore,
University of Minnesota Physics












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