Matrix Multiplication...

*To*: mathgroup at smc.vnet.net*Subject*: [mg23551] Matrix Multiplication...*From*: "J.R. Chaffer" <jrchaff at nwlink.com>*Date*: Sat, 20 May 2000 03:10:27 -0400 (EDT)*Organization*: Northwest Link*Sender*: owner-wri-mathgroup at wolfram.com

Hi, New to Mathematica, and to exotic matrix techniques. Apparently Mathematica does "ordinary" matrix multiplication via the "dot" product symbol, "."; but when one uses the asterisk, one gets "squaring" of two matrices: If m1 = {{a,b},{c,d}}; and m2={{e,f},{g,h}}; then m1*m2 = {{ae, bf},{cg,dh}}, and m1*m1 = {{a^2, b^2},{c^2, d^2}}; while m1.m2 gives normal matrix multiplication. What is going on here? What kind of matrix multiplication is this "*" giving? Why does it match up with the casual appearance of 'squaring' if m1 = m2? I tried the Mathematica function "Outer", i.e. "Outer[Times,m1,m2]", and this is NOT the same as the result with "*". I don't understand outer products anyway, but apparently that is not this, whatever it is. Can someone give me a short explanation? Thanks. John Chaffer old-timer-new-person