22 lines
689 B
R
22 lines
689 B
R
#' Tensor Mode Crossproduct
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#'
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#' C = A_(m) t(A_(m))
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#'
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#' For a matrix `A`, the first mode is `mcrossprod(A, 1)` equivalent to
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#' `A %*% t(A)` (`tcrossprod`). On the other hand for mode two `mcrossprod(A, 2)`
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#' the equivalence is `t(A) %*% A` (`crossprod`).
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#'
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#' @param A multi-dimensional array
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#' @param mode index (1-indexed)
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#'
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#' @returns matrix of dimensions \code{dim(A)[mode] by dim(A)[mode]}.
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#'
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#' @note equivalent to \code{tcrossprod(mat(A, mode))} with around the same
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#' performance but only allocates the result matrix.
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#'
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#' @export
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mcrossprod <- function(A, mode = length(dim(A))) {
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storage.mode(A) <- "double"
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.Call("C_mcrossprod", A, as.integer(mode))
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}
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