fold: General Folding of Matrix

In rTensor: Tools for Tensor Analysis and Decomposition

Description

General folding of a matrix into a Tensor. This is designed to be the inverse function to unfold-methods, with the same ordering of the indices. This amounts to following: if we were to unfold a Tensor using a set of row_idx and col_idx, then we can fold the resulting matrix back into the original Tensor using the same row_idx and col_idx.

Usage

fold(mat, row_idx = NULL, col_idx = NULL, modes = NULL)

Arguments

mat	matrix to be folded into a Tensor
row_idx	the indices of the modes that are mapped onto the row space
col_idx	the indices of the modes that are mapped onto the column space
modes	the modes of the output Tensor

Details

This function uses aperm as the primary workhorse.

Value

Tensor object with modes given by modes

References

T. Kolda, B. Bader, "Tensor decomposition and applications". SIAM Applied Mathematics and Applications 2009.

See Also

unfold-methods, k_fold, unmatvec

Examples

tnsr <- new("Tensor",3L,c(3L,4L,5L),data=runif(60))
matT3<-unfold(tnsr,row_idx=2,col_idx=c(3,1))
identical(fold(matT3,row_idx=2,col_idx=c(3,1),modes=c(3,4,5)),tnsr)

Example output

[1] TRUE

rTensor documentation built on May 15, 2021, 9:06 a.m.