```Date: Jun 17, 2013 6:14 AM
Author: Murray Eisenberg
Subject: Re: Working with arrays

Just use plain old "." (period).CenterDot has no built-in meaning, as DocumentationCenter page ref/CenterDot explains. You could give it the meaning of Dot by using the Notation package, but that would merely provide a bit of notational proximity to the usual mathematical notation at the expense of the annoyance and traps of the package.On Jun 16, 2013, at 5:19 AM, amannucci <Anthony.J.Mannucci@jpl.nasa.gov> wrote:> I thought I understood variables. This sequence completely mystifies me:> Clear[lA, xtest]> lA = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};> xtest = {4, 5, 6};> lA\[CenterDot]xtest (* First case *)> {{a, b}, {c, d}} . {x, y} (* Second case *)>> The output is:>> {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}\[CenterDot]{4, 5, 6}>> {a x + b y, c x + d y}>> How do I force matrix multiplication to actually occur, as in the second answer? Why does Mathematica do the matrix multiply in the second case but not the first?>> Thanks for any help.>> -Tony---Murray Eisenberg                                    murray@math.umass.eduMathematics & Statistics Dept.      Lederle Graduate Research Tower            phone 413 549-1020 (H)University of Massachusetts                               413 545-2838 (W)710 North Pleasant Street                         fax   413 545-1801Amherst, MA 01003-9305
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