kronecker {base} | R Documentation

## Kronecker products on arrays

### Description

Computes the generalised kronecker product of two arrays, `X` and `Y`. `kronecker(X, Y)` returns an array `A` with dimensions `dim(X) * dim(Y)`.

### Usage

    kronecker(X, Y, FUN = "*", make.dimnames = FALSE, ...)
    X %x% Y

### Arguments

`X` | A vector or array.
`Y` | A vector or array.
`FUN` | a function; it may be a quoted string.
`make.dimnames` | Provide dimnames that are the product of the dimnames of `X` and `Y`.
`...` | optional arguments to be passed to `FUN`.

### Details

If `X` and `Y` do not have the same number of dimensions, the smaller array is padded with dimensions of size one. The returned array comprises submatrices constructed by taking `X` one term at a time and expanding that term as `FUN(x, Y, ...)`.

`%x%` is an alias for `kronecker` (where `FUN` is hardwired to `"*"`).

### Author(s)

Jonathan Rougier, J.C.Rougier@durham.ac.uk

### References

Shayle R. Searle (1982) Matrix Algebra Useful for Statistics. John Wiley and Sons.

### See Also

`outer`, on which `kronecker` is built and `%*%` for usual matrix multiplication.

### Examples

    # simple scalar multiplication
    ( M <- matrix(1:6, ncol=2) )
    kronecker(4, M)
    # Block diagonal matrix:
    kronecker(diag(1, 3), M)

    # ask for dimnames

    fred <- matrix(1:12, 3, 4, dimnames=list(LETTERS[1:3], LETTERS[4:7]))
    bill <- c("happy" = 100, "sad" = 1000)
    kronecker(fred, bill, make.dimnames = TRUE)

    bill <- outer(bill, c("cat"=3, "dog"=4))
    kronecker(fred, bill, make.dimnames = TRUE)

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