Re: Matrix Dot Product

*To*: mathgroup at smc.vnet.net*Subject*: [mg52189] Re: [mg52159] Matrix Dot Product*From*: "David Park" <djmp at earthlink.net>*Date*: Sun, 14 Nov 2004 04:30:37 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

You're in luck! Mathematica will do it. Here are two sample 2 x 2 matrices. matA = Array[a, {2, 2}] {{a[1, 1], a[1, 2]}, {a[2, 1], a[2, 2]}} matB = Array[b, {2, 2}] {{b[1, 1], b[1, 2]}, {b[2, 1], b[2, 2]}} Then matrix multiplication is just performed with the 'dot' product. matA.matB {{a[1, 1] b[1, 1] + a[1, 2] b[2, 1], a[1, 1] b[1, 2] + a[1, 2] b[2, 2]}, {a[2, 1] b[1, 1] + a[2, 2] b[2, 1], a[2, 1] b[1, 2] + a[2, 2] b[2, 2]}} Check out Help/List and Matrices/Matrix Operations for more information and examples. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: MacDonald, Calum (MAT) [mailto:C.A.MacDonald at gcal.ac.uk] To: mathgroup at smc.vnet.net Hi I was wondering if someone could please help me with a command for calculating the dot product of two (NxN) matrices. For example, for two (2x2) matrices, A and B, we define the dot product as: A(1,1)*B(1,1) + A(2,1)*B(2,1) + A(1,2)*B(1,2) + A(2,2)*B(2,2) i.e. we multiply corresponding entries of the matrices and sum these values. It is easy to write this in a loop but for large matrices the calculation is rather slow. Is there a Mathematica function that I can call that will allow me to do this faster? Thanks Calum