Re: mathematica newbie question

*To*: mathgroup at smc.vnet.net*Subject*: [mg66897] Re: mathematica newbie question*From*: "David W.Cantrell" <DWCantrell at sigmaxi.org>*Date*: Sat, 3 Jun 2006 03:25:17 -0400 (EDT)*References*: <e5osv8$i51$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

"Jeremy Watts" <jwatts1970 at hotmail.com> wrote: > Hi, > > Just trying to get to grips with Mathematica and matrices. Why is it > when I enter :- > {0, 0, 0}, {1, -1, -1}, {-1, 1, 1}}^2 > > then Mathematica returns :- > > {{0, 0, 0}, {1, 1, 1}, {1, 1, 1}} > > and not {{0,0,0},{0,0,0},{0,0,0}} (the actual square of the matrix) as > I'd have expected? > > Is it treating what I entered as separate vectors or something, and not > an actual matrix? Something like that. In[9]:= matr={{0, 0, 0}, {1, -1, -1}, {-1, 1, 1}} Out[9]= {{0,0,0},{1,-1,-1},{-1,1,1}} In[10]:= matr^2 Out[10]= {{0,0,0},{1,1,1},{1,1,1}} In the above, it merely squared every element (inside the inner lists). In[11]:= matr matr Out[11]= {{0,0,0},{1,1,1},{1,1,1}} Here, it multiplied elementwise, so to speak. The result was the same as Out[10] since we were multiplying matr with itself. But of course, these were not what you wanted. You need to specify a specialized matrix operation, rather than expecting Mathematica to recognize somehow that that is what you want. Here are two ways: In[12]:= matr . matr Out[12]= {{0,0,0},{0,0,0},{0,0,0}} In[13]:= MatrixPower[matr,2] Out[13]= {{0,0,0},{0,0,0},{0,0,0}} David Cantrell