MathGroup Archive 2013

[Date Index] [Thread Index] [Author Index]

Search the Archive

Working with arrays

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131190] Working with arrays
  • From: amannucci <Anthony.J.Mannucci at jpl.nasa.gov>
  • Date: Sun, 16 Jun 2013 05:19:15 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Delivered-to: l-mathgroup@wolfram.com
  • Delivered-to: mathgroup-outx@smc.vnet.net
  • Delivered-to: mathgroup-newsendx@smc.vnet.net

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



  • Prev by Date: HTML output
  • Next by Date: Re: Getting the plotted data from a graph
  • Previous by thread: Re: HTML output
  • Next by thread: Re: Working with arrays