fold: General Folding of Matrix
In jamesyili/rTensor: Tools for tensor analysis and decomposition

Description Usage Arguments Details Value References See Also Examples

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.

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

`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

This function uses aperm as the primary workhorse.

Tensor object with modes given by modes

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

unfold-methods, k_fold, unmatvec

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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)