tensr (version 1.0.1)

mat: Unfold a matrix.

Description

mat returns a matrix version of a provided tensor.

Usage

mat(A, k)

Arguments

A

An array to be unfolded.

k

The mode, or dimension, along which the unfolding is to be applied.

Value

A matrix whose rows index the \(k\)th mode and whose columns index every other mode. The ordering of the columns is in lexicographical order of the indices of the array \(A\).

Details

Applies the matrix unfolding operator (also called 'matricization' or 'matrix flattening' operator) on a provided tensor. There are multiple ways one could do this. This function performs the matrix unfolding described in Kolda and Bader (2009).

References

Kolda, T. G., & Bader, B. W. (2009). Tensor decompositions and applications. SIAM review, 51(3), 455-500.

Examples

# NOT RUN {
A <- array(1:8, dim = c(2,2,2))
mat(A, 1)
mat(A, 2)
mat(A, 3)
# }