Re: Working with arrays

*To*: mathgroup at smc.vnet.net*Subject*: [mg131207] Re: Working with arrays*From*: Tomas Garza <tgarza10 at msn.com>*Date*: Mon, 17 Jun 2013 06:28:32 -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>

Strange, indeed. I get the same result as you report. Yet, In[7]:= Dot[lA, xtest] Out[7]= {32, 77, 122} as it should. Perhaps it has to do with the way one enters the dot. If you use an ordinary dot (not the center dot) from the keyboard it gives the right answer: In[10]:= lA.xtest Out[10]= {32, 77, 122} -Tomas > From: Anthony.J.Mannucci at jpl.nasa.gov > Subject: Working with arrays > To: mathgroup at smc.vnet.net > Date: Sun, 16 Jun 2013 05:19:15 -0400 > > 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 >

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