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MathGroup Archive 2000

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Re: RE: Kronecker product of matrices

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21406] Re: [mg18502] RE: [mg18429] Kronecker product of matrices
  • From: Gianluca Gorni <gorni at dimi.uniud.it>
  • Date: Tue, 4 Jan 2000 02:12:37 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

> Kostas Oikonomou  wrote:
> ------------------------
> 
> Is there a simple way to make Outer[Times,A,B] produce the Kronecker
> product of A and B?  What I mean is that if A is nxn and B mxm, Outer
> produces a block form, instead of a plain (mn)x(mn) matrix.
> 
> -------------------------

If you need the Kronecker product as an (mn)x(mn) matrix here is a way:

kroneckerProduct[a_?MatrixQ, b_?MatrixQ] :=
 Flatten[Map[Flatten[#1, 1] &,
   Transpose[Outer[Times, a, b], {1, 3, 2}], {2}], 1];

I found the (hopefully) right transposition by trial and error.

Another way is to build blocks and then merge them with BlockMatrix[],
from the package LinearAlgebra`MatrixManipulation.

Good luck,

                Gianluca Gorni

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