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.edu

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