Re: Matrix Dot Product

*To*: mathgroup at smc.vnet.net*Subject*: [mg52178] Re: [mg52159] Matrix Dot Product*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sun, 14 Nov 2004 04:30:14 -0500 (EST)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

Use Plus@@Flatten[A*B] dim={2,2}; A=Array[a,dim]; B=Array[b,dim]; Plus@@Flatten[A*B] a[1, 1]*b[1, 1] + a[1, 2]*b[1, 2] + a[2, 1]*b[2, 1] + a[2, 2]*b[2, 2] dim={2,3,2}; A=Array[a,dim]; B=Array[b,dim]; Plus@@Flatten[A*B] a[1, 1, 1]*b[1, 1, 1] + a[1, 1, 2]*b[1, 1, 2] + a[1, 2, 1]*b[1, 2, 1] + a[1, 2, 2]*b[1, 2, 2] + a[1, 3, 1]*b[1, 3, 1] + a[1, 3, 2]*b[1, 3, 2] + a[2, 1, 1]*b[2, 1, 1] + a[2, 1, 2]*b[2, 1, 2] + a[2, 2, 1]*b[2, 2, 1] + a[2, 2, 2]*b[2, 2, 2] + a[2, 3, 1]*b[2, 3, 1] + a[2, 3, 2]*b[2, 3, 2] Bob Hanlon > > From: "MacDonald, Calum \(MAT\)" <C.A.MacDonald at gcal.ac.uk> To: mathgroup at smc.vnet.net > Date: 2004/11/13 Sat AM 04:40:07 EST > To: mathgroup at smc.vnet.net > Subject: [mg52178] [mg52159] Matrix Dot Product > > 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 > > > >