Re: Working with arrays

*To*: mathgroup at smc.vnet.net*Subject*: [mg131201] Re: Working with arrays*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Mon, 17 Jun 2013 06:26:31 -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*References*: <20130616091915.825D36A2D@smc.vnet.net>

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 at 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 at 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

**References**:**Working with arrays***From:*amannucci <Anthony.J.Mannucci@jpl.nasa.gov>