RE: simple vactor magitude question

*To*: mathgroup at smc.vnet.net*Subject*: [mg43787] RE: [mg43754] simple vactor magitude question*From*: "David Park" <djmp at earthlink.net>*Date*: Sat, 4 Oct 2003 02:05:06 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Nathan, I'm not certain that I completely understand your question. Here I take a simple vector and set p[i] values from it. vector = {a, b, c, d}; Do[Set[p[i - 1], Part[vector, i]], {i, 1, 4}] Checking it... vec = Table[p[i], {i, 0, 3}] {a, b, c, d} Now using your expression... Sum[p[i]*i, {i, 0, 3}] b + 2 c + 3 d it seems to work all right, but it is not the conventional magnitude of the vector. This could have been done more easily with vec.Range[0, 3] If you really want the magnitude you should use... Sqrt[vec . vec] Sqrt[a^2 + b^2 + c^2 + d^2] David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Nathan Moore [mailto:nmoore at physics.umn.edu] To: mathgroup at smc.vnet.net Suppose I generate a 1-d vecctor of "N" numbers, p[i], and now I want to find the sum of (the vector element * index). I think the syntax should look something like, Sum[p[i]*i,{i,0,N}] but this doesn't seem to be the correct syntax - any help would be appreciated. Nathan Moore, University of Minnesota Physics