Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Topic: Working with arrays
Replies: 4   Last Post: Jun 20, 2013 4:03 AM

 Messages: [ Previous | Next ]
 Murray Eisenberg Posts: 2,105 Registered: 12/6/04
Re: Working with arrays
Posted: Jun 17, 2013 6:14 AM

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
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2838 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305

Date Subject Author
6/17/13 Murray Eisenberg
6/17/13 Bob Hanlon
6/17/13 Tomas Garza Hernandez
6/20/13 collabe