# [R] Kronecker matrix product

Berwin A Turlach berwin at maths.uwa.edu.au
Wed Jul 13 11:37:37 CEST 2005

```>>>>> "RH" == Robin Hankin <r.hankin at noc.soton.ac.uk> writes:

RH> I want to write a little function that takes a matrix X of
RH> size m-by-n, and a list L of length "m", whose elements are
RH> matrices all of which have the same number of columns but
RH> possibly a different number of rows.

RH> I then want to get a sort of dumbed-down kronecker product in which
RH> X[i,j] is replaced by X[i,j]*L[[j]]

RH> where L[[j]] is the j-th of the "m" matrices.  For example, if

RH> X = matrix(c(1,5,0,2),2,2)

RH> and

RH> L[] = matrix(1:4,2,2)
RH> L[] = matrix(c(1,1,1,1,1,10),ncol=2)

RH> I want

RH> [,1] [,2] [,3] [,4]
RH> [1,]    1    3    0    0
RH> [2,]    2    4    0    0
RH> [3,]    5    5    2    2
RH> [4,]    5    5    2    2
RH> [5,]    5   50    2   20

> tmp <- sapply(1:length(L), function(j, mat, list) kronecker(X[j,,drop=FALSE], L[[j]]), mat=X, list=L)
> do.call("rbind", tmp)
[,1] [,2] [,3] [,4]
[1,]    1    3    0    0
[2,]    2    4    0    0
[3,]    5    5    2    2
[4,]    5    5    2    2
[5,]    5   50    2   20
>

HTH.

Cheers,

Berwin